The injury came late on
Turns out, Garvin's block is illegal, although no flag was thrown on the play.
According to the NFL rules, "It is a foul if a player initiates unnecessary contact against a player who is in a defenseless posture," and that includes "A kicker/punter during the kick or during the return." There's more: "Forcibly hitting the defenseless player's head or neck area with the helmet, facemask, forearm, or shoulder, even if the initial contact of the defender's helmet or facemask is lower than the passer's neck and regardless of whether the defensive player also uses his arms to tackle the defenseless player by encircling or grasping him" is prohibited.
Put another way: Garvin can almost certainly expect to be fined.