Bottleneck ratings and beating players above your level

I've been quite obsessed with chess for the past 3 years and have had a steady progress from 600 to 1500 elo. I view chess purely as entertainment, but try to patiently grow my rating and keep a track of my progress. I usually grind one time control at a time until I break into the next 1xxx elo and then move onto another time control, usually also switching back and forth between chess.com and other chess sites.

I recently found the "open challenge" option in live chess and to my surprise, I've been able to beat opponents with considerably higher rating than mine in blitz and rapid. Taking into account how long it took me to get to 1500, I was certain that I would get totally obliterated by anyone above 2000 every single time.

Is it possible that people are stuck at a certain chess rating because of being stuck in a particular playing style or opening meta, and not just because of inferior chess abilities? I've had devastatingly hard games (and losses) against 900s and wins against 2000s because of one-move blunders.

When I play against someone with a lower rating, I get thrown off by weird opening moves and not being able to punish their mistakes, especially in blitz. Suddenly we are in a really weird, untheoretical position and I end up winning for making less mistakes, but not because I knew what I was doing. Is it possible that when I play against a 2000, I make such horrible moves that the opponent gets confused and ends up losing?

Here's an example of a quite horrendous 5|0 blitz game against a 2000.

I removed the opponents name out of respect.

This has a total of 8 blunders according to stockfish, which feels something that shouldn't happen at this level. I've also won a bunch of games before move 12 against opponets above 2000. I've made sure that the players are legit and not engine users. Shouldn't you already be near to immune against blunders to get to and maintain this rating? Are the opponents playing bad on purpose after seeing my rating?

tl;dr why are lower rated players (that aren't cheating) sometimes tougher to beat than opponents at your current rating level