Because that's the kind of things immature guys joke about since we were little kids. Has nothing to do with homosexuality. In my case it wouldn't anyway.
I'm sorry but a guy wearing a pink jump suit (anywhere, not just the Super Bowl) isn't common. I can't recall ever seeing it and it would catch my attention for sure. Now is he wrong for wearing a pink jump suit? Of course not, but if you are my friend and a male, gay or straight, you're getting clowned for wearing a pink jump suit.
a lot of things said to friends though are not appropriate in a public forum like twitter.