Pretty good demonstration of the mechanics of how bumping the slide can cause the striker to drop. The guy takes the gun apart and shows which components contribute to this malfunction. Worth a watch if you're curious what's happening internally.
It seems pretty clear that there are a lot of differences between P320s in the wild, so it's hard to generalize these findings well. This guy's gun isn't stock, and I personally have not been able to reproduce this behavior on mine (which is stock). It does seem more and more that the 320 design does not tolerate non-spec parts well, which is especially weird given the design was supposed to be modular.