Vale, Martin Gardner.
I expect this is a journalistic simplification:
In his philosophical writing Mr. Gardner rejected speculative metaphysics because it could not be proved logically or empirically.
as Gardner surely knew that Popper refuted this position a long time ago. The argument would have been familiar to him, being roughly a diagonalisation: this predicate ("can be proved logically or empirically") refutes the scientific process as a truth-producer just as readily as it refutes metaphysics. Thus one needs some kind of transcendent (speculative?) account of knowledge that cannot be purely logical or empirical. Kant is turning in his grave.