Giving this person all of the doubts and then some: Chicken often get fed estrogen to force their growth. I believe, traces of this estrogen can still be found in the meat. And then there was also a myth that this estrogen could affect the cup size, in both women and men.

So, maybe there’s some half-knowledge of a myth in there and that’s why their misbelief, that avoiding estrogen makes them manly, somehow lead them to cut out chicken meat…?

To give any source at all, this looks like a pretty comprehensive discussion, although no idea if it is trustworthy: https://featheredfarmlife.com/chicken-and-hormones-separating-fact-from-fiction/