Basically he is a horney male who wants to mate with any female anywhere, he doesn't care if she is pregnant or not. He is smelling her because she smells different being pregnant.
Watch out because your female can get pregnant AGAIN while still pregnant with the first batch of kittens and she could have TWO seperate litters. Why isn't your male neutered yet? Please get him in right away and KEEP THEM APART until you do or you will have more babies then you know what to do with. Get your female spayed too as soon as she is done with the kittens. Please do NOT let them outside either.