If this is an apology, it doesn’t sound very sincere! The tone seems more like he’s sorry he got caught for his blunder than that he truly understands what was so wrong about it. And I get it if he doesn’t understand why the phrase is so offensive to Native Americans, but I’m not sensing that he has any interest in learning why. Just sounds defensive.
Whatever it meant to him personally, that is still not what the phrase actually represents. Being inaccurate and/or ignorant doesn’t excuse the fact that it was blatantly racist to put that phrase on a shirt with no other context. I’d be more impressed if he took responsibility for the mistake and used it as an opportunity to learn. Too bad that neither he nor the Gap are handling this debacle with much sensitivity or thoughtfulness.