I'm wondering if that's an NFL rule/interpretation because Pereira said the same thing on Twitter.
Doesn't look like the pylon is OOB, here's the two rule definitions for Touchdown and OOB
"ARTICLE 1. TOUCHDOWN PLAYS. A touchdown is scored when:
(a) the ball is on, above, or behind the plane of the opponents’ goal line (extended) and is in possession of a runner who has advanced from the field of play into the end zone
(b) a ball in possession of an airborne runner is on, above, or behind the plane of the goal line, and some part of the ball passed over or inside the pylon
(c) a ball in player possession touches the pylon, provided that, after contact by an opponent, no part of the player’s body, except his hands or feet, struck the ground before the ball touched the pylon
(d) any player who is legally inbounds catches or recovers a loose ball (3-2-4) that is on, above, or behind the opponent’s goal line"
"SECTION 21 OUT OF BOUNDS, INBOUNDS, AND INBOUNDS SPOT
ARTICLE 1. PLAYER OR OFFICIAL OUT OF BOUNDS. A player or an Official is Out of Bounds when he touches a boundary line, or when he touches anything that is on or outside a boundary line, except a player, an official, or a pylon."
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I don't think there's clear evidence that the ball crosses over the pylon, hence why they said the play sands. However he wouldn't have been OOB when he hit the pylon.