I'd be surprised if it wasn't a significant statistical aberration. A 12% or so drop across the league seems big. You'd have to get all the data but I'm not in the mood.
Of course, every so often they tweak the rules and how the game is officiated, so it's not unusual for totals to jump from year to year.
If you ask me, it looks like decent evidence to support the idea that a lot of discretion is being used when calling holding.