πολλοί τραπεζῶν, οὐ φίλων εἰσιν φίλοι =
many tables aren’t of the friends, they are friends.
I’m missing some key grammatical point.
πολλοί (masc. nom.) doesn’t modify τραπεζῶν (fem gen.).
Many [men] are friends of tables, not of [their supposed] friends.
The idea is that many men who profess to be friends are really interested in getting free meals from their supposed friends. This makes sense in the context of the ancient Greek and Roman worlds, where rich men entertained a large crowd of “friends” at their dinner tables, and where some men made professional careers as parasites (παρα+σιτον), eating at the tables of rich men for whom they professed friendship.
This is an iambic trimeter, probably taken from a comedy, which you may be able to identify by pasting the Greek in Google. It may be from an extant or fragmentary comedy, or it may be a line quoted by Stobaeus, a Byzantine scholar who compiled a large number of one-liners from earlier literature. My guess is that, unless it’s from a sizeable fragment of an extant play, it’s attributed to Menander.
Another very similar one, that I came across on papyrus just the other day, is
πολλοι τραπεζης ουκ αληθειας φιλοι.
There were various collections of such single-line iambics (monostichs) made in antiquity. To judge from papyri they were used in schools, doing double duty as moral pabulum and writing exercise for schoolchildren, or rather schoolboys: a depressingly large proportion of them are misogynistic. A big Byzantine collection of them is traditionally known as the Menandri Sententiae (“Maxims”), Gk. Γνῶμαι. Some of them do in fact come from Menander, ripped out of context, but by no means all.
Stobaeus’ 5th-century work was pitched at a higher level. He anthologized larger and more meaningful extracts from across the entire range of Greek literature, organized by subject-matter and with authorship identified.
I shouldn’t have suggested this comes from Stobaeus, and he’s not as late as I thought. When I wrote “attributed to Menander” I meant “attributed (probably falsely) to Menander.”