When asking a "who" question about the past, do you normally default the verb to masc if you don't already know that the answer will be all female?
"Kto" is grammatically masculine (and "co" is grammatically neuter), so even if you were asking such a question in an all-girls boarding school, it would still have to look like that.
I think that would be an acceptable sentence in English but in a quite specific context. Like: John didn't believe him, Jane didn't believe him, Mark didn't believe him, so who DID believe him? We rather don't accept such constructions.