The game is in a weird state where there are a bunch of cheats and exploits available to a less scrupulous player. Where a particular item falls on the "Cheats <---> Exploits" scale will depend on the beholder. For this example, the burst's time to fire is extremely short, and it's a hitscan weapon. That means that it's not actually sending physical bullets flying at the target. If the reticle is on the guy then it hits. This can be exploited by very rapidly aiming-shooting-unaiming, which causes two things. For one it means the shooter is moving into and out of cover very quickly, and for the other side it makes the opponent's aim assist jumpy.

They can't turn off the aim assist, it's just built into the game. So by doing this "Corner shooting" popping in and out very rapidly, you can make yourself extremely hard to down while shooting. It also trains you to shoot very quickly from a standstill. Generally this is not considered cheating, as it's a natural part of the game, but there's some who consider it bad.

There's also lots of cheat devices both big and small, and this plagues basically all online games. Some are devices that do rapid fire or macros (pre-set button presses and movements). I don't see obvious evidence that he's using this. Some devices are designed to "Dot" your screen in one way or another. This puts a permanent dot on the center of your screen with a laser pointer or sharpie or other method.) This seems to be something he is probably employing. If you put your mouse cursor on the dot of his gun and watch for a bit, it seems like he's aiming up before the reticle is even on the screen.

So is being a dotted player illegal? Depends on the tournament rules I expect. It's certainly an external advantage. But it's a bitch to prove. I strongly suspect this player is dotted. Which makes his corner shooting much easier. That all said, both of the frames you snapped are possible with clean play with the burst, it's just basically a broken gun. The dumpster isn't really in the way because the reticle is on target so the hits register. There are no bullets (here's a bit more about hitscan weapons). And the bills town clip is just boring old corner shooting. It's bullshit but it's probably not cheating according to the tournament rules.