Die-cast models are usually cast from a zinc-aluminum-magnesium-copper alloy. Cannot comment on the level of ferromagnetism, but both zinc and copper are diamagnetic... I seem to recall, though, that €-cent coins are only magnetic because of their steel core...
I think if they added an amount of steel or iron to the alloy, that might explain magnetism.
EDIT: Oh yes, and that little car is beautiful.