who is this blatantly cheating idiot

[Guilhermeziat]

Lol no, people who specialize in MAing often get silly scores like that, especially when playing index.
Coming from an index player myself: the barrier between comboing and MAing a certain stream on a certain bpm is VERY small. It's also super hard to lose form when playing, especially on this level of skill, so what happens at best is you miss an arrow and then cbrush that column consequently. Index is all about brute force and stamina, the rest comes natually.