It is falsifiable if you consider that a simulation would have limited resources allocated to it. The null hypothesis would be the universe runs in a way where a simulation couldn't cheat by performing a rough calculation at the hard parts, thereby spending a tiny fraction of what would be needed and produce the same observable result.

The idea that quantum fields exist in multiple states simultaneously until observed become evidence for a simulation, since a simulator could be deferring calculations on things not observed.

Also, the very program this article is referring to could be considered as evidence for it, since if a rough simulation can be made where the observable result is indistinguishable from a result where every atomic element in the entire universe was simulated, then, again, a simulator with limited resources would make do.

The law of conservation of energy is built the same way. There is no way we can test ways that energy is transferred that we don't yet know about, but this law is still considered true, because we have so many examples of it working.