It looks to me that each cell is two letters [ A K ], so if one wishes to go to that cell, then CMD + A + K would put the mouse in the center of that cell. Letting go of CMD would close the overlay and the mouse is just there in that space, while pressing Space before letting go of CMD would cause a mouse click event. If one wishes for greater mouse precision, after typing CMD + A + K and holding CMD there, a smaller grid of letter squares are displayed within the original cell; typing the matching character in the sub-cell moves the mouse to that even more specific point.

Or it might not be holding CMD, I could be wrong. Here's a better and shorter video explaining it: https://www.youtube.com/watch?v=A2rmvlOz5l0