I think that was the quote
Well I think this kind of confirms that Jack finds out that he's related to Claire. Or it could be something done by the writers to make us
think that he knows
(damn writers making me paranoid
)
But if he does know it would explain a few things. Like why he didn't want to see Aaron around about the time of 'Eggtown'; possibly because the thought of Aaron reminded him of his father's infidelity. Bringing up painful memories, perhaps?
The real question is though, if Jack
does find out that Claire is his half-sister, who tells him? I'm pretty sure Ben will know because he knows everything, so there's a possibility he would tell him. Maybe Claire turns up after disappearing with Christian Shepard and tells him? Maybe Christian Sherpard tells him himself? I don't know if anyone else actually cares about this, but personally I find it intruiging