I don't think he meant truth in terms of marketing (although I'm hard-pressed to think of a case where Apple has outright lied in their ads, but maybe in a release) but truth as design fundamental.
Based on the context of that sentence I would say Gruber meant it more in the way of "truth to materials" (http://en.wikipedia.org/wiki/Truth_to_materials) in which Apple's design is reductive and efficient to the user. No ornament beyond the materials that construct the product.
Based on the context of that sentence I would say Gruber meant it more in the way of "truth to materials" (http://en.wikipedia.org/wiki/Truth_to_materials) in which Apple's design is reductive and efficient to the user. No ornament beyond the materials that construct the product.