One way to look at is that currently we only have data on the correlation between her tail twitches and falling objects, but not on the causation involved.

Given this we have two scenarios "Something about her tail twitches causes things to fall" or "Items falling can cause her tail to twitch in the past."

The first option is actually more consistent with the known physics of the world, as it doesn't require anything thought to be impossible like precognition or backwards causation. And it would fit pretty closely to the known phenomena of ponies using magic, often involving them moving their bodies, to move distant objects. So it is plausible she is performing subconscious magic.

I agree that this might cause difficulty in testing, however I suspect it could be done via, say, letting the cutie mark crusaders try to harvest all the apples in Applejack's orchard. Lots of things would be falling in presumably dangerous and unpredictable (and thus tail-twitch-inducing) ways.

Of course, what algorithms work to induce twitching is the first thing to be studied in any case.

But given the base rates of tail-twitches and falling objects ...

(I just watched the first episode of this show. I'm not sure why I'm impressed with it ....)