Can two male kittens mate?

I know this is a strange question, but i got two kittens from the same litter, their both nearly 3 months now, we were told they were a boy and a girl and consequently named them fergie (boy) and freyja (girl), just now i noticed freyja mounting fergie and trying to mate with him....so i checked online to see how to identify a boy and a girl, it turns out i have two males (which is a shock to the system!) and i was curious why freyja was trying to mate with another boy? :o/ any suggestions?