If you check out gender and sexuality centric websites/forums you'll find that it's pretty universally accepted that gender and sexuality are completely unrelated. In certain ways they can be, if your friends are referring to the fact that most cis people are straight (which is obviously because of reproductive purposes), that is true, but once you start looking at the trans and non-binary spectrum, you'll find them to be completely irrelevant. I've seen just as many gay/lesbian trans people as I have straight, and plenty of pan/omni/bi/femme/masc uline/etc. sexuals thrown in to the mix! I'd love to do a survey so I could make a scatter plot of physical sex, gender identity, and sexuality, it would probably look crazy