It suggests that such a meta-ability might exist, but doesn't prove anything. It's also possible that these abilities are discrete but are correlated because they're subject to selection as a package... sort of like how physical coordination and endurance are probably selected for at the same time.

In any case the existence of such a meta-ability doesn't mean intelligence is one dimensional unless you re-define intelligence so as to exclude everything that can't be tied to that ability.

It is also possible, but there's no evidence for it. There's no evidence for any of Gardner's work. The biggest criticism of his work is that there's no empirical basis for the classification of his "intelligences." Gardner even admits to this, saying the choices are the work of an "artistic judgment" [1].

[1] https://en.wikipedia.org/wiki/Theory_of_multiple_intelligenc...