If one, however, goes out of their way to harass transexual people when stating this preference, then yeah, it's a bit transphobic. Intention matters.
I'd say it is a probably a minority position but it is a genuinely held one
Whoever brought it up has some deep unresolved issues, however. Or was fishing for an argument.
EDIT: It's like fetishes. Preferences are fine and should be respected, but they're also better kept off private. Telling people of a specific ethnicity you're "into them" is also kinda creepy.
This was in the context one of those kink quizzes regarding what things someone was into, so genders, fetishes, bodily features, sex acts, etc. It isn't like someone just announced to a bar "I'd never date a transperson" out of nowhere.
I wonder what their position is towards someone who prefers trans people.
They'd consider it fetishism, unless said person was also trans and only preferred other trans people because of wanting that shared life experience.
Their point was that thinking of trans women as different to women as a group was inherently bigoted.
I think that depends on your social circle.
https://www.bbc.com/news/uk-england-57853385 has some examples of people for whom this was clearly not a strawman as of 5 months ago.