Sam2:
We Pasken they’re not Jewish because otherwise a Jewish girl that receives Kiddushin from a Goy would need a Get MiSafek.
Couldn’t we just say kol d’porish meiruba porish?
(I hope that’s the right expression.)
Also, it is a highly unlikely scenario that a non-Jew would give a girl kiddushin in such a way that it would be valid if he were a Yid. Are we really choshesh for that?