He specifically said work ethic in addition to toughness.
I think it's very arguable. The fact that Aldridge isn't a very good rebounder or post scorer is much more likely to be an issue of talent, rather than toughness. I think it's much more plausible that he simply isn't good at those things than that he's simply frightened.
The idea that rebounding and inside play only requires "toughness" and, therefore, anyone who doesn't do it lacks toughness is silly, IMO. Rebounding and post scoring is every bit a skill/talent as anything else, like passing, shooting, etc. If Aldridge lacks those skills/talents, he could be as tough as anyone and still not do well at those things.