But being certified or not doesn't have anything to do with it—you can misunderstand the principles of Scrum just fine on your own. Arguably, certified Scrum Masters would be more likely to actually understand them given their training. And there's a huge difference between "project manager" and "Scrum Master", and if you've met someone that claims to be able to fill both roles in the same team then they're either misunderstanding Scrum horribly or they're that one rare unicorn that managed to make it work that one time.

(And, in case you're interested, "certified" is the standard term. In case you're not interested, my apologies for bringing it up.)