That's correct. With DAS tuning it's much less frustrating to play at the speed at which you can think. Here's one of the top online players of puyo puyo tetris, for reference.
Yep it's a human - there's a good number of people who can reach that speed but it takes years of practice. I believe a lot of the community started young on various platforms so some people have been playing 10+ years
https://youtu.be/7AjbWroX4vA?t=18m57s