A lot of people really can't comprehend men being bisexual.
You see it all the time on Twitter/Tiktok when the topic of "DL" men comes up. You have tons of (usually women) asking why these men can't simply be openly gay and date guys, ignoring the fact that the vast majority of DL men are mostly-straight bi men who occasionally crave cock but are otherwise almost exclusively attracted to women. At least in the West in 2025.
Obviously I can't comment on this guy in particular but when a woman says she "found out" her ex was gay/DL it usually means he's bi (and sometimes not even that, it might mean he likes trans women and/or pegging and/or crossdressing).