This may mean nothing more than that the only rocket bomb attacks described in the book itself as close to Winston occur when Winston goes for a walk in the prole quarters.
There was a roar
that seemed to make the pavement heave; a shower of light objects pattered
on to his back. When he stood up he found that he was covered with
fragments of glass from the nearest window.
and while he and Julia are slipping off for a tryst, possibly in prole quarters
They were passing in silence down a side-street (Julia would never speak when they were away from the main streets) when there was a deafening roar, the earth heaved, and the air darkened, and Winston found himself lying on his side, bruised and terrified. A rocket bomb must have dropped quite near at hand.
Also, the proles have a casual term for them, as Party Members do not, which could indicate a familiarity. From the same scene:
'Steamer' was a nickname which, for some reason, the proles applied to
rocket bombs. Winston promptly flung himself on his face. The proles were
nearly always right when they gave you a warning of this kind. They seemed
to possess some kind of instinct which told them several seconds in advance
when a rocket was coming, although the rockets supposedly travelled faster
Other descriptions are far off that could have landed in prole quarters
Somewhere far away a rocket bomb exploded with a dull, reverberating roar. About twenty or thirty of them a week were falling on London at present.
The rocket bombs crashed oftener than ever, and sometimes in the far distance there were enormous explosions which no one could explain and about which there were wild rumours.
As though to harmonize with the general mood, the rocket bombs had been
killing larger numbers of people than usual. One fell on a crowded film
theatre in Stepney, burying several hundred victims among the ruins. The
whole population of the neighbourhood turned out for a long, trailing
funeral which went on for hours and was in effect an indignation meeting.
Another bomb fell on a piece of waste ground which was used as a playground
and several dozen children were blown to pieces
Somewhere in remote distance a rocket bomb thundered.
That is, the conclusion that the rockets land only in prole quarters has some evidence but not conclusive proof.