I guess it's just supposed to be a brute strength push? Hence the name. It's Normal-type instead of Fighting because there's no finesse or technique to it. Just moving rocks, any normie that lifts enough can do that.Somewhat related: What does Strength as a move actually entail thematically? For 6 Generations it was only learnable by TM, and in Gen 8 it was put in the natural movepools of some Pokemon you'd associate brute force with like Mudsdale, Bewear, and Copperajah.
The complication here is that in Gen 7 it was only naturally learned by Machamp, and the description across many games including Gen 8 describes it as a Punch, when 2/5 natural learning lines don't have arms (and Pinsir seems more like it'd fight with its head than punching things). Also, while the "push, stop, push, stop" animation makes sense with this, it's funny to imagine the Boulders being punched into place Chris Redfield style.
The punch thing is probably some weird translation snafu, especially considering the move isn't boosted by Iron Fist.