Never believe anything you read from coaches or the media when talking about rules. This was NEVER about 11 on and 11 off. If that's what Coach Smart thought was the issue in 2017, he is completely wrong. The actual issue is players leaving the field and returning during the same dead ball period or substitutes entering and then leaving during the same dead ball period.
This is one of those things that's a foul in both NFHS and NCAA rules, but in most cases, it's hard to keep track of which players and leave and enter on each dead ball. It's much more obvious in a situation like this. It's still rarely called though, especially now with the substitution match-up rule in NCAA. I've learned this week the B1G/MAC supervisors have told their crews not to call it in a situation like this, but the SEC. In that regards, Coach Smart was correct in his statements. He's the co-chair of the NCAA rules committee so he should know it better than he does, but this is something that comes up rarely.
This very specific play though was not an issue with this rule however. The reason is because there was an officials time out for replay review. That means anyone that enters the field after the review can become replaced players. There was a review so that's why the crew would not have a flag here even if they were enforcing the rule as written. That's an example of subtlety I wouldn't expect a coach to know.
When situations like this happen, it's likely to be a point of discussion with the rules committee. If nothing else they need to get the conferences on the same page. I wouldn't be surprised to see the NCAA drop the rule entirely since the substitution match-up rule make it obsolete. If Notre Dame had done it too late in the play clock and the play clock expired while Georgia was matching up, that would be a delay of game foul on the offense. You'll notice the U stayed on the snapper telling him he couldn't legally snap it, but backed away with plenty of time left on the play clock.