The vet told us our baby is a male.

However, tonight Proton started displaying some weird behavior that
I've never seen in a male cat before.

My BF and I were playing with Proton then suddenly he started doing
this weird meow/purr and putting his bum in the air.
My BF exclaimed suddenly, "I think Proton may be a little girl!"

I looked up some pictures online...and I think Proton has the vertical
slit that is supposed to indicate female cat but I'm not sure.

Has anyone ever encountered that kind of behavior in a male kitten/cat?

Again: Proton is rubbing his face on everything especially my BF's hands, making a weird vocalization he has never made before, bum is in the air with tail up exposing his anus and genitals.

Sorry if I seem silly asking this.