The argument is either 1) the receiver wasn't defenseless (I suppose there is gray area there, but by rule when in doubt it is a foul) 2) Nacua wasn't "delivering a blow" and was trying to make a tackle (why then were his arms behind his back?), or 3) He didn't make forcible contact to the head or neck area (forcible isn't a precise term, so reasonable people can disagree, but again when in doubt it is a foul).  Or 4) they don't understand the rule and make some other argument.

Anyway, in my opinion, if you're going to go crazy on the sideline and cost your team 15 yards, you better be 100% right.  When you do it after the replay booth confirms a call on the field, all the refs just think you're an idiot and tune you out the rest of the game.  

I never officiated above the high school level, so I've never officiated a game with replay, but when a coach goes crazy over anything that isn't an obvious error, the coach loses all respect and credibility in the eyes of the officials, and that hurts his team.