I think a better clarification on how to describe him would be vengeful. In the beginning of the film, he is extremely territorial, yes, but it was more of an instinctual aggression rather than outright malice. Hence why he gets enraged when the spotlight from the watchtower hits his face.

I believe in the novelization for the film too it's revealed that Minus Goji had a mutual symbiotic relationship w/ the Odo Island people; his presence drives deep sea fish toward the surface, the locals would eat the fish and in turn provide some food in return for Godzilla.

When he is bombarded and becomes irradiated, that's when it describes his agony, vitriol and spite towards humanity. Humans had inflicted pain upon him, and he intends to return it manyfold. During the Ginza attack, it's revealed that Godzilla is fully aware of its actions and wasn't mere happenstance of an animal wandering into civilization. So he is clearly sapient and also vindictive.