Certainly. Just as humans come with a wide variety of personalities, so too do pokémon. It’s just that the ones we often hear about, such as incineroar’s aggression, are merely the behaviors displayed by the majority of individuals of a particular species; it doesn’t mean that there is no minority.
Besides, the only time you should worry about a pokémon’s personality is when it poses a threat either to the pokémon’s own well-being or the well-being of those around it. (As a note, I don’t just mean hyperaggression, either. Although, yes, an overly aggressive pokémon is worrying, what may be even more worrying is lethargy—especially lethargy that cropped up seemingly out of nowhere—as that may indicate actual health problems.)
In other words, there’s really nothing wrong with your incineroar. He’s simply tame, anonymous.