NFL Clarification - Offsetting Penalties

[Mark Dexter]

I believe this was in the Washington-New Orleans Game. I'm sure the officials administered it correctly, but I'm interested in what the rule is nonetheless.

A2 holds back at the line of scrimmage. After A1 runs out of bounds, he is hit by B1, who is flagged for a late hit personal foul. The R said that the penalties offset and that the down would be repeated.

Few questions:
What is the NFL rule on dead ball fouls? Is there some time limit, or was this considered a double foul because it was still 'part of the play' even though the runner had stepped OOB?

In NFHS, we'd penalize both fouls, right? Go 10 yards back from the spot of the hold, then go 15 yards forward from that point (the succeeding spot). A would either repeat the down, or be awarded a new series, depending on where the ball was after the defensive penalty was marked off.