TL;DR: The other difference between epic and drama, according to Aristotle, is that epic is in hexameter and drama is in multiple metres.

Let’s look at what Aristotle is trying to do in the Poetics. The first sentence of the work is a abstract of the whole:

I propose to treat of Poetry in itself and of its various kinds, noting the essential quality of each; to inquire into the structure of the plot as requisite to a good poem; into the number and nature of the parts of which a poem is composed; and similarly into whatever else falls within the same inquiry.

_{Aristotle (circa 335 BCE). Poetics 1447a. Translated by S. H. Butcher (1895). The Poetics of Aristotle, page 7. London: Macmillan.}

The highlighted clause indicates that Aristotle intends to present a classification or categorization of poetry, a division of poetic works into genera and species, as he does for abstract concepts in the Categories, virtues and vices in the Ethics, and living things in the History of Animals. The categorization that he comes up with is thus determined by the examples that fell under his study. In particular, he does not discuss prose fiction as there were as yet no examples in Greek. (The earliest surviving Greek novel is Callirhoe from the 1st century CE, and there are fragments from the Hellenistic period.)

Aristotle identifies three aspects of poetic works by which they can be classified.

They differ, however, from one another in three respects,—the means, the objects, the manner of imitation being in each case distinct.†

_{Poetics 1447a.}

_{† The terms that Butcher has translated as “means” (ἑτέροις), “objects” (ἕτερα), and “manner” (ἑτέρως) are all inflections of the same word, and mean “by a different means”, “a different thing”, and “in a different manner” respectively.}

First, the means, that is, the metre:

People do, indeed, commonly connect the idea of poetry or ‘making’ with that of verse, and speak of elegiac poets,† or of epic (that is, hexameter) poets; implying that it is not imitation that makes them poets, but the metre that entitles them to the common name.

_{Poetics 1447b.}

_{† Poets employing elegaic metre, consisting of alternative hexameter and pentameter lines, not writers of elegies.}

Second, the objects, that is, the characters:

Since the objects of imitation are persons acting, and these persons must be either of a higher or a lower type (for moral character mainly answers to these divisions, goodness and badness being the distinguishing marks of moral differences), it follows that we must represent men either as better than in real life, or worse, or as they are. […] Homer, for example, makes men better than they are; Cleophon as they are; Hegemon the Thasian, the inventor of parodies, and Nicochares, the author of the Deliad, worse than they are.

_{Poetics 1448a.}

Third, the manner, which we now call the narrative voice:

There is still a third difference—the manner in which each of these objects may be imitated. For the means being the same, and the objects the same, the poet may imitate by narration—in which case he can either take another personality as Homer does, or speak in his own person, unchanged—or he may imitate by making all his actors live and move before us.

_{Poetics 1448a.}

The essential differences between epic poetry and tragic drama, in Aristotle’s view, are a difference of metre (the one is in hexameter and the other is in multiple metres) and a difference of narrative manner (in the one there is a narrator who tells the story, and in the other the characters speak for themselves):

Epic poetry agrees with Tragedy in so far as it is an imitation in verse of characters of a higher type. They differ, in that Epic poetry admits but one kind of metre, and is narrative in form.

_{Poetics 1449b.}

He goes on to describe a further difference, in the extent of the action:

They differ, again, in length: for Tragedy endeavours, as far as possible, to confine a itself to a single revolution of the sun, or but slightly to exceed this limit; whereas the Epic action has no limits of time.

_{Poetics 1449b.}

However, he notes that this is not an essential difference between epic and tragic dramas, but rather the most suitable form of each, in his opinion. For some tragedies employed the same freedom of action as the epic:

though at first the same freedom was admitted in Tragedy as in Epic poetry.

_{Poetics 1449b.}

Even in the case of metre, Aristotle indicates that some poets wrote long works in multiple metres, though he does not like the result and so does not include these works under his category of “epic”:

Still more absurd would it be to mix together different metres, as was done by Chaeremon. Hence no one has ever composed a poem on a great scale in any other than heroic verse.† Nature herself, as we have said, teaches the choice of the proper measure.

_{Poetics 1447b.}

_{† That is, dactylic hexameter.}