Does Sans hate Undyne? Was she the one who caused his injury?

“hate? nah. in fact, i’d love to give her a big ol’ hug for caving my skull in. made my life much easier.”
He scoffs, sending you a bland look.
“i don’t hate her, no. we never got along, not really, and i don’t really appreciate the head trauma… but she keeps it together for pap, and that’s asking a lot, in this place. she gets some brownie points for that.”