I think some people look to hard to get offended. If we refrained from EVERYTHING that anyone or any group found offensive, it would be a humorless and drab world. Playing
is she or isn't she is a far cry from shouting "->-bleeped-<-" and pointing. I myself look for humor everywhere and I have definately found plenty stuff regarding TG/TS to laugh about, including myself, even if it means laughing to keep from crying.
We are a statistical oddity and breaking gender norms will always get peoples attention (at least in our lifetime). If you don't pass, people will notice and you are likely to be the topic of discussion be cause we are.....interesting. Hell, when I'm with my BFF Melissa, we play that game too (is she or isnt she?) and I'd say most of you are lying if you said you havent done the same.
As TS, we are hyper aware of gender cues (as are people that work with us professionally) and we are more capable of putting the clues together to ascertain if someone has or is trying, to breach the gender divide. Your new friend sounds lke a nice girl with a good sense of humor.