it's very possible, and it's very narrow-minded, and a confusing paradoxon, but when I find it in a person, it's usually a sign of immense insecurity (as is homophobia in general, I guess?) - transmen who don't want to be confused with lesbians (neither do I but I'm not taking it out on lesbians...), transwomen whom society sadly at times thinks of as gay men in drag......
In order to define their identity, many people need something to set themselves apart from....the most effective way to set oneself apart from something is to ridicule and degrade it and proclaim that you don't understand it...
While homophobia sickens me wherever I see or hear it, I understand that my parents and grandparents grew up in a different world...a homophobic world. I understand to a certain extend that it may be harder for them to shake off their resentments than it is for my generation. Doesn't make their opinions any less awful... but yeah. When I meet a 20-year-old homophobic transman, I just want to send him back to the hole he crawled out of.