I don't trust sbt and would like nothing more to say yes that is proof of him cheating but it's not, a second or so before he does a stand still combo at an area that's very likely for a player to be when using a grapple, you can hear a second grapple sound(the first one being a team mate).
Also it was noxfox aka haxxy he killed, I'm willing to bet he was after sbt the entire game, he does the same thing to me when I play and is too dumb to change how he chases you.
Try this video editor it's easy enough to use for cutting junk out of clips: https://shotcut.org/
Stop playing at 60fps you are just making it harder on yourself playing with such bad settings, even if you don't have a 144hz, 240hz monitor your mouse inputs & movements will be more responsive at higher fps. PS5 games can do 120fps for a reason.