percentiles way off??

my son just had his 15-month check-up the other day and the NP said he was 98% for height and 86% for weight. when we got home, i punched the numbers into some online calculators and they all said he's 41% for height and 68% for weight... why is it so different?? and he really doesn't seem like he's shorter than average. we were at the airport the other day and he ran over to a window where some other little kids were looking at the planes, and he was only maybe 2-3" shorter than a kid who was easily a year or two older. my husband and i are also both pretty tall. they measured him at 31" and 26 lbs (but they also keep him clothed and in his diaper, and i don't know if that is messing up the weight).

i'm including some pictures to give an idea of his height and weight just by looking at him.








the last pic is him next to his cousin, who is three weeks younger but was born six weeks early.