If a supernatural event occurred, how would you tell?

[Welsh cake]

Two reasons. One is that most people do not define the term as you do and classify as natural anything not made by people. The second is that the term 'unnatural' carries negative connotations, often without a good reason.

I fail to see how that ultimately matters. Does "non-natural" make you happier then?

"Physical" is not a totally clear term, either, but I do think it is harder to confuse, and there is no negative/positive paradigm between "physical" and "non-physical".

I'd argue that non-physical makes even less sense than "supernatural". Everything is physical, material, even imaginary concepts are all down to brain chemistry otherwise it does not, cannot, exist. Entities should be by definition, physical. A non-physical entity is a contradiction.

*reads wiki*

An entity is something that exists by itself, although it need not be of material existence.

Are you shitting me? What kind of moronic statement is that?

Actually you know what? Fuck humans and their silly backward babble gobbledygook they dare to call a "language".