He didn't defend rape. He objected to the use of the term "sexual assault", because the "assault" part connotes the use of violence. He doesn't believe any violence was used by his friend. Based on his understanding of the situation, the girl probably acted willing to his friend, and his friend likely didn't know her true age (can
you tell a 17yo from an 18yo??). So he objects to his friend being called a violent rapist when he's really likely only guilty of having sex with a legal minor, while believing she was there of her own free will and probably of legal age.
Finally, your use of the word "rape" is wrong anyway. Having sex with a minor isn't "rape", it's "statutory rape", and that's only in the US. US laws do not apply worldwide. The age of consent varies from place to place, and according to UK residents on this forum, it's only 15 or 16 there. So are you going to tell me that everyone in the UK that has sex with someone that young is a "rapist"? Sorry, no.