So it's possible. There are physiological trends that happen in gay men.
Gay men have a very high chance that their index and ring fingers are approximately the same length. Sounds daft, but it's a real thing and it occurs in relatively few straight men. It has something to do with the environment in the womb at a particular stage of development that may also be linked to the expression of same sex attraction. Possibly. These things are very hard to study.
It's also true that gay men are far more likely to be a second child, particularly a second son. Obviously this isn't universal it's just a bump in the statistics.
As someone mentioned above penis size studies are notoriously unreliable for a number of reasons and it's entirely possible that gay men are likely to report a larger dick size (eg. lie) in the same way that 20-30 year olds seem to have bigger dicks than 30-40 year olds in some of these studies.
So it's plausible, but I'd say far from proven.