The twos and the existing ones. I made a reasonable guess that proved to be correct. All the twos had symmetry and can be plotted on the grid like a tile patt

The twos and the existing ones. I made a reasonable guess that proved to be correct. All the twos had symmetry and can be plotted on the grid like a tile pattern...and every increasing number in a row is two positions to the left of the lower number. It was blatant at that point in the vid. Right at around 12:14 and then confirmed by the 18 minute mark.