“Nothing happens unless it has an explanation within the laws of physics” is an assumption; if it was broken then it would be broken. The mountain would be inexplicably gone, not explicably gone.
In that hypothetical, there could be testable proof of "a magic event occurred" without magic becoming part of science.
That said, in the cut and thrust of conversation and or debate the example by dialogue isn't perhaps as clear cut a device as it may have seemed from your keyboard.
That might just be my reading <shrug>
Yes, I get your point...