Like no social cue whatsoever...but [sorta spoiler alert] I'm like 100% sure he didn't kill teach's dad. He wouldn't lie to TEACH.
He didn't know who his dad was so how he could tell for sure that he didn't kill him â•®(￣▽￣)â•
You think he wouldn't know if he killed someone at teach's house...? In fact, teach probably did something to his own dad,before guwon even got there. That's why his brain deleted the memories to protect himself from trauma, as a response he subconsciously tries to hurt others in his sleep.
Guwon is dumb as hell big chunk of muscles