Nurk is averaging this year almost exactly what he averaged during the Nurk Fever 20 games and for the 2nd half of last season. If it wasn't for him struggling at the beginning of last season then he's been pretty consistently good the whole time he's been here. The only major improvement is that he is much more comfortable running the offense at the top of the key (or at least Stotts allows him to do it more this year).
He's cleaned up a lot of his bad habits but it's not Most Improved Player worthy when he's basically doing the same things just gradually improving on all of them.
Edit: While it corresponds with a jump in minutes there is a huge difference in production with Siakam, Hield, and Fox this year.