You're right. It is complaining about gossip that you heard second-hand. Had you overheard it yourself, then complaining would be reasonable. You didn't and it isn't.
Why would you? It isn't.
It is not internalized homophobia to be offended comments like this any more than it would be internalized misogyny if a woman was offended because similar comments were made about her choice in trainers.
Let it go. Also, you did just get it off your chest - you told us.