Thats what Penn Wagers said, but thats not what happened, and thats not even the rule:
Horse Collar Tackle
ARTICLE 15. All players are prohibited from grabbing the inside back collar of
the shoulder pads or jersey, or the inside collar of the side of the shoulder pads
or jersey, and immediately pulling the ball carrier down. This does not apply
to a ball carrier, including a potential passer, who is inside the tackle box (Rule
2-34). Note that the tackle box disintegrates when the ball leaves it.
As this pic shows, he had a handful of pad:
No the picture shows a handful of jersey. I do see where it says collar of jersey also, but I'm guessing they didn't call it because of his arm being around the body and the jersey grab not being the sole attempt to bring him down.