Your "admirer" sounds like a pretty messed-up, sad guy.
I hope this experience doesn't make you think that all, or even 99.9% of, gay men are as socially maladjusted as this one pathetic guy is.
If I were to meet an attractive, muscular, cool, laid-back, 40 year-old,
unmarried, DENTIST (my GOD!

) who was chatting me up in a social situation I'd probably, just probably, assume he just MIGHT be family...
Call it a hunch!
Having a healthy self-esteem (and being a 270 lb. Rugby player) I, however, would just have asked you if you were gay, and if so would you like to grab a Pint sometime after work.