For the longest time, Lucas said Han was just blowing smoke at Obi-Wan in an effort to impress him, but Obi-Wan sees right through it (look at his face and reaction during that scene). Then, some EU author decided they would explain this off hand remark and everyone started to believe that explanation, mostly because they think it makes more sense. I for one don't think it needs an EU explanation and I don't think it was a writer screwing up. I think Han was trying to impress Obi-Wan. Again, watch Obi-Wan's reaction and then watch what Han does. Immediately after that he says "She's fast enough for the old man" like he knows he's been caught by him.
Anyway, that's my take. I don't have anything else to add though.