Probably the magnetic field induces a current in the molten aluminum that in turn creates a magnetic field in opposition, and that squirts the metal out?
Copper is also non-ferrous but if you do the experiment where you drop a strong rare-earth magnet down a copper tube, it doesn't fall normally, but sort of floats downward, and I think it's the same principle. The moving magnet causes a current in the copper pipe, which causes a magnetic field in opposition to the falling magnet. It's neat to see...
-- Dave