Yes, shroud does hold the record for most kills in a pubg game. He broke it in March 2018 when he killed 27 players in one game. He killed 8 players within the first 25 seconds of landing into the game.
However, we do not know whether that is the fastest or not. However, it is important to know that he did practice a lot which is why he was able to pull it off. A good kill rate without any hacks or people dying on purpose is about 23 kills per game. However, this can increase slowly as you get better at the game.