It could very well be the latter. My son is used to getting to the rim (ok, quite a ways under it) but in playing more competitive AAU, there are a lot more (good) bigs so he needs to pull up more - could be a parallel there with college centers vs. the monsters in the NBA. Nuggets beat write TJ McBride has tweeted about how much he likes MM's floater.
It's a tough shot - easy to shoot long but in the NBA it works for Monte.
Get him working on a little half hook in addition to the floater!