If i recall correctly, you're that 1300 psr guy who payed for VIP, no?
Whatever, i'll answer your questions in a straightforward manner for you to understand. First of all, NC exp gain were lowered to promote lanes. Secondly, as i see on the logs, Yurnero was simply farming efficiently and maximising hes farm while no one disturbed him, it's normal for this to happen, there are some players with 0 denies, unbelievable.
As for the PSR part, if the 1800 guy won the game, he would've gain +1, he can do +/- 5 in a game where all are 1600-1700+, also you, if you've won the game +23 instead -, the psr system is kinda simple, all you have to do is to have a over 50% win rate to climb the ladder, of course, the psr gain/take reflects the game you are in, if the game is overall high for you, the gain/take is higher.
I hope this street-like explaining helps you understand.
Regards.