The Walton hold was much more of a hold than the one on Mahoney. That could actually be argued that it was a ticky-tack call, but one that is occasionally made. The problem was that it was on the other side of the play and had zero impact in the outcome. The one on Mahoney was absolutely not a hold in any alternate universe.
I'm pretty close with an NCAA official, he's young and working his way up so he's a Line Judge in the MEAC right now and we speak often about the nuances of refereeing. He's told me every play is analyzed by the head of officials and you're graded on penalties you do AND do not throw. He told me that if, for example, he's the Line Judge on the right side of the field, and a quick screen is thrown to the left, and he throws a flag on someone right in front of him that is not incredibly, excessively blatant, he's dinged for that. The officials only want to impact the game if the foul directly impacts the play, which of course makes sense. I just thought it was pretty cool that they coach these guys to stay out of the way as much as possible.
But then again, Jeff Flanagan threw that flag. He and his crew are widely known as some of the worst officials in the country.