It's an impressive achievement, but it does seem to get stuck at times, like from around 1:35 to 2:10 and 3:45 to 4:30 (irritatingly on the edge of two screens), but that second time actually resulted in a new key showing up, which the article says was a flaw in the emulation that it was exploiting.

Interesting that their approach didn't work for Pitfall (never played Gravitar).