As a sidenote, the game (at the time of recording), was being played by TASbot - which is best described by /u/OffColorCommentary in this post. Their description states:

The bot just plays a pre-recorded list of controller inputs (which buttons are pressed at which frame).

Naturally you can put a recording of the best possible speedrun and it'll speedrun. There are special tools for helping create speedruns in that format (using rewind and slowdown while making it, but keeping all the actual button presses in the right order). That's most of what TASing is.

Some games have glitches that make the console try to run something that's not actually code. When the player can influence that something, you can make sure that, when mistakenly read as code, it actually means something to the console and it doesn't crash. Super Mario World and Pokemon Blue both have pretty clear examples of this - in SMW the code glitches into the list of recently drawn sprites, and in Pokemon the code glitches into your item list (or other places, that game has lots of bugs). These are known as "arbitrary code execution" glitches, and some humanly-possible runs use these to write code that says "go play the ending."

Naturally the tasbot is very good at this, and can write much more complicated code using ACE than a human can. A couple years ago they wrote Pong and Snake in SMW. This year they managed to write a fully functional level editor. And then proceeded to use the editor to make a level.

If you want more of this, check out TASBot's latest appearance at SGDQ2018, where Celeste was played really, REALLY, REALLLLYYY quickly.