he can be both.
he is a straight male.
he has sadistic desires.
that's his sexuality.
...the world is full of guys like that who don't become rapists. full of them. they have consciences, they either resist entirely or use BDSM as a way to get off. controlled sadism with a willing partner.
he is a rapist.
that's a violent criminal.
...you need to distinguish between desire and action. if desire were a crime, i would be locked up as the biggest serial killer in history! but i have a conscience with prevents me from acting on my desire to kill the stupid arseholes who park on the pavement, block the supermarket aisle, neglect their kids, etc, etc, etc.
maybe that is the difference. i wouldn't classify him as heterosexual, his orientation has been render null and void. he's sexual impulse/desire is based on pathology. he's a sadistic rapist.
is the same case with paedophila. they have no orientation. whatever caused it, their sexuality never developed. all sexual desire has been pushed aside by their phillia.