Thanks to TwinsNorth49, hopefully I have this figured out. Fair disclaimer, the angle isn't the greatest. Here we go. In this photo, shortly before the ball is there, the plate appears to be wide open (potentially top corner closed, but a clear running path is available). Fraction of a second later, foot covers the top section of the plate, but middle and back corner are left open. Fraction of a second later, catcher has the ball, and the plate appears to be blocked. I can see the argument against this play (and the rule certainly benefits the catcher), but he had the ball, and then moved to block the plate. By rule, this seems allowable.