Short Circuit happens when the unit senses too much instantaneous current draw, like what would happen if you plugged in a power cable with its wires crossed. It’s a best guess and the engineers do their damndest to make it represent only an actual short circuit.
But it’s not perfect. Though it’s pretty danged close. Which is why you rarely hear of it occurring.
In the case where you have the warning but do not have an actual short circuit there can be several reasons, but most of them are pretty obscure. For example, turning on a piece of power hungry gear right at the top of the sine wave. Or the opposite,
where the incoming power has a momentary glitch right at the exact moment one of your connected pieces is pulling peak power.
In any case, it’s not possible to say exactly why, but it can be safely said that it is a rare occurrence and generally not one to worry about.
On the positive side, there have been quite a number of actual short circuited cables Power Plants have detected and helped customers identify. And I know of a few that had intermittent shorts in the cables and the unit protected just as it should.
Bottom line, it may happen on occasion but it should be rare if you don’t actually have a problem and it sounds like you do not.