What training does your T have in critical thinking and applying scientific methods? That's a serious question. It looks like a complete b*ll*cks thing to say, if you pardon my saying so - I can poke three huge holes in that theory without even trying: 1) the clients who come to see her have psychological issues or they would not be going to therapy, and being neglected by your mother is a pretty common and important cause for psychological issues; 2) she made no mention of non-gay female clients, which makes the statement valueless; and 3) it's completely unscientific to formulate a general theory from a few isolated cases, and conversely it's a very basic principle that while you can sometimes say general things about a whole population ("Finnish people have a tendency toward introversion"), it is not valid to make specific statements about an individual based on those general things ("you're Finnish, so you must be an introvert").

Your T does not seem like a bad T in general, and I'm sure she's a good person, but this particular thing was ill-advised and my opinion is that you don't need to pay any attention to her "maybe you crave closeness because you were neglected" statement if it doesn't ring true for you.