introducing kitten to dog behaviors

Hi. Have a 2 yr old Westie and am slooowly inroducing her to new male
kitten ~9 weeks. I am leashing dog and correcting when dog lunges etc.
Dog seems excited and not aggressive no barking or growling. Cat sees
dog and will avoid but not cower or hide. I want them to get to know
each other but the dog now that I let them close is sort of nudging,
nibbling the cat...she will also take her nose and flip the cat over
and nudge etc mostly in the crotch area of cat....the cat has NOT
freaked at any of this, he has batted at dog a couple of times, hissed
a bit; and when dog had him pinned he was not trying to escape, just
sort of flailing around...am I dense or is/are he/she/they playing? Or
is it dinner time for Westie? I have a good hold of the leash and
correct when this happens but the cat doesn't seem to be being harmed.
I figure cat would freak if he was getting hurt.