I have the rule book up and I don't see anything about how fast the play developed in regards to the catcher blocking the plate. The closest thing I can find is: "....if the catcher blocks the pathway of the runner in a legitimate attempt to field the throw (e.g., in reaction to the direction, trajectory or the hop of the incoming throw, or in reaction to a throw that originates from a pitcher or drawn-in infielder)"
Only thing that might apply there is if it was a throw from a drawn-in infielder, but a) I don't think the 1B was drawn in, and b) the throw was coming from the first base side, anyway.