Without the actual rules, I can't say one way or the other if they made the right call or not. But I'm not going to just take the word of the NFL that's what the rule book says. I think the ref screwed up, didn't stop play before the subsequent snap, and then tried to fix the mistake by making up the rule on the fly. Since there was a riot, the NFL sure as hell isn't going to come out now and say the ref made a mistake, they're going to cover for him.
I'd love to read exactly what the rule book says about replay and when it can be done.
I take it the only reason for a buzzer is for this very instance - a review by the officials in the booth. If correct, then the three refs on the field were negligent in not immediately blowing their whistles in reponse to the buzzer. Technically, the buzzer stopped the play, so by not blowing their whistles, regardless of what point the play had progressed to, the field refs violated their own procedures.
The real problem is with NFL rules. The rules have been almost continuously changed to squeeeze in more commercials and make game times consistently fit in the three hour window. Whose stupid idea was it to have the ref gallop after the ball at the completion of a play to spot it for the next play. The only reason is to predict game durations. I've seen this potentially affect several outcomes. College rules are more sensible. Clock stops temporarily to spot the ball (and, as appropriate, move the chains), then the 25 second clock starts. Fair for everybody, no unrealistic pressure on the refs, no room for complaints about how the ref should have hustled. With the college rule, if this was indeed an equipment malfunction (highly unlikely), this probably would not have happened as the short interval between plays would have allowed time to sort it all out.