First off, no that’s just his handle it’s not literally a dog playing Tetris.
Rebirth happens at about the 1:21 mark. It’s absolutely insane that the first killscreen happened less than a year ago and back then rebirth seemed like a pipe dream. Not just the endurance and skill, but knowing all the unique, unseen situations he needed to avoid in the higher levels in order to not trigger a killscreen. And some of those levels have a lot of conditions that will trigger one.
For those unaware of what this means: because of the way NES Tetris is programmed, eventually the levels will functionally loop back around to level zero again. Hence why the speed suddenly goes from hyper speed to beginner mode.
I found a YouTube link in your post. Here are links to the same video on alternative frontends that protect your privacy: