Wasn't this already proven by Bell's Theorem?

For the most part, but violations of Bell's inequality can also be explained by action at a distance. The impossibility result in this paper is nevertheless really old. For example, conditional swap tests are well studied and incompatible with any statistical interpretation of the wave function (in the same slightly stronger sense of this paper). There are experimental results that invalidate these interpretations quite directly. The view of the wavefunction as a reflection of statistical ignorance has not been tenable for a very long time. The interesting thing here is the non-trivial attention part.