Also, according to Mike Johnson, he was 2nd in defensive plays per game behind Bergeron last season. Not sure what that entails exactly or where he gets his stats from, but he said that on TV.
I have seen an article showing plays away from the puck - it was an article about Tavares as he headed into free agency - and among the players shown, Matthews was either first or second (to Bergeron) in every category. Loose puck recoveries (in the OZ, DZ and NZ), pass blocks, shot blocks, stick checks. If you added the categories up, Matthews came a sliver behind Bergeron, with both far ahead of the others. I don't know how inclusive the data set was, and it only showed six players (and I found a couple more in another article bringing the total up to around ten). I assume it is a private data set. I also don't know if it was the same data set or the same categories as Mike Johnson used (I doubt it as the totals were different). Doesn't matter as these stats are not public (or at least I have never been able to find them).
However, I have said before that at even strength Auston Matthews blocked the third most shots per game last year among forwards (behind Boone Jenner and Tom Pyatt). No other high end forwards anywhere near. The closest were Kopitar and Wheeler. Matthews blocked 50% more.
Compared to the other young offensive stars he is on a different level defensively. This shouldn't surprise anyone who actually watches him play.