The information points to a separation of the jobs of publisher/retailer on the one hand and the techical work of printing on the other.
For a long time after the invention of the printing press, the same person could be both printer and bookseller. William Caxton, who probably brought the printing press to England, not only printed and sold book, but also printed some of his own works (mostly translations). When you look at other early printers, such as Wynkyn de Worde (Caxton's successor) and Richard Pynson, the terms printer and publisher appear to be used interchangeably, although the technical jobs of creating type, typesetting, bookbinding etc. are of a different nature than e.g. regularising spelling, arranging the creation of illustrations or arranging contracts.
There is an interesting comment in the Wikipedia article on William Jaggard, a contemporary of Shakespeare:
In their era, most members of the stationers guild were either printers or booksellers; both were businessmen with their own establishments, journeymen and apprentices, though in anachronistic modern terms printers could be regarded as blue-collar while the booksellers were white-collar retailers. Most commercial publishing was done by booksellers, who chose their books and commissioned printers to print them.
In the 19th century, some people still combined the jobs of printer, publisher and bookseller, e.g. John Baxter (1781–1858, known for his Baxter's Bible). However, Edward Chapman, William Hall and the company they founded are just described as publishers, not printers. (Chapman & Hall published Dickens, Thackeray, Robert Browning, Trollope, ...)
According to Walter Thornbury, writing about Paternoster Row at the end of the 19th century,
Before the close of the eighteenth century the house of Longman and Rees had become one of the largest in the City, both as publishers and book-merchants.
Printing is not mentioned here. I assume that Longman & Co outsourced the technical work of printing, in this case to Thomas Davison.
