A good friend of mine, finding out I wasn't straight, told me, "I gotta hand it to you Andy, you tried really hard." I've got a set of what some might call masculine hobbies, and have none of the affectations of what some might consider gay.
Turns out that being gay means I'm attracted to and form intimate relationships with people of the same sex as me. So the "I never would have guessed" response is like, yeah, how would you guess who I'm attracted to any better than you'd guess my favorite food?
I enjoyed reading this and really like your description and how you set up the classroom story - interesting and engaging, as well as an important point!