I was there too. And I also wonder.
I'm pretty sure that a crossdresser is not 100% straight. I know it's debatable and for a lot it's a fact that you can CD and be 100% straight. What I can say for sure is that I'm not and I have not been 100% straight ever in my life. Never ever had sexual intercourse with another man or making out, not even touching. I don't find porn appealing, gay or straight. If I'm horny I may have an erection watching either but I don't think that's an accurate measurement of straightness.
Deep inside, I know I'm bi at least. Never went for it, never tried. I'm sure that, given the opportunity, I would have tried it in my teen years or even later. I had my opportunities with girls, took some, pass some. When I entered into young adulthood I was already in a committed relationship and that put a closure to the issue.
There are many factors. Homosexuality was (still is in some ways) a stigma, sex was a taboo topic. The opportunities may have been there but nobody were advertising and I never had the initiative, for the same reasons probably. It's really hard to tell. The criteria used to define an homosexual are not based on facts mostly. Of course you can see that a man having actual intercourse with another man is homosexual. But there is that idea that in prison a man penetrating another man is not. So, the line is actually a wide gray zone.
In the end... does it really matter?