You can't call someone a racist just because they are not sexually attracted to black guys.
It's like calling someone a misogynist because they are gay.
The analogy isn't accurate. And I think you're right. Expressing that preference, especially only when asked doesn't make you a racist. Just like saying you only like men doesn't make you misogynist (keeping in mind being gay incorporates the idea that women aren't sexually of interest whereas gayness doesn't inherently mean melanin level preference... that's a personal choice).
However, when a gay guy makes puking gestures and carries on about the idea of a vagina... I'd say that's at very least internalized misogyny. The same way as putting something in writing on a profile about dislike of Black men is a bit racist (and often a lot depending on how it's worded).
I'll use myself as the example. I grew up in a very white part of the world. Also a very racist part of the world. I discovered through close friendships and discussion that what I thought was just a preference actually had deep cultural roots and was self hatred a bit too for being brown myself. I realized I was 100% comfortable with Black women (to the point of sleeping with them easily...far more easily than white women) but completely afraid of Black men. This pointed to something being not quite right.
So after working on it I found that my deep inner core perception was based in my racist upbringing and culture. It wasn't intentional nor even consciously expressed. But it was there. So I worked to change it because I wanted to. Was I racist? Yes on some level. Was it my fault? Not really. Not working to change would have been.
You know you best. I'm not suggesting you're the same. I'm offering my experience as something to consider.