He's never really been a high level prospect coming up so expectations are low. I think he's a solid college player but doesn't really look like he's got an NHL frame unless he fills out. That's fine if you've got the kind of puck skills that Jackson Blake has, but that doesn't seem to be Rizzo's game. Plus, he a low round pick who hung around Junior A before college. When you never play major junior, you tend to fly under the radar.
Also, lots of guys score in college who don't stand a chance in heck of carrying that to the pro level. So ... yeah. We'll see. Another similar player is Kevin Wall at Penn State. Similar background, although he's American, similar production in college.