I have the same thoughts. I feel like the author really wants to make Guwon a MAJOR red flag that you can't help but like a little and have confusing feelings for (as a reader)
What if when guwon found them teach was the one who begged guwon to save him from his father/kill the father but just forgot?
What if Teach actually killed his father and somehow Guwon was there to witness or help, but Teach just forgot?
Oh my god even that could have happened
I get an odd feeling that Guwon killing Teach’s father was actually a good thing. The first few chapters really painted out his dad to be evil or a villain to Teach, and I feel like his memory isn’t that great considering how out of touch with reality he was when his head was injured. I feel like Guwon isn’t revealing to him that part because Teach said he wanted to remember for himself and confront things