Just a random fan here...
but aren't half the teams going to trend above average for penalties and half below?
Is there a graph showing the top 5 most penalized?
If the Saints are always one of the top 5 consistently over that many years, it would be more compelling evidence.
But also, it could just be a coaching mindset as well to play more aggressively or to coach into the grey area more than another coach.
To really determine that you would need to analyze a lot of plays of when holding should have been called and wasn't to see if some teams are getting called more and also getting away with more non-holding calls.
Interesting graph, but I think more data needs to be shown.