I don't think Littlefoot intentionally meant to offend his Grandpa. He was just defending Doc, and I think it's nice that he admires Doc. Given Doc's mysteriousness and awesomeness, it's only natural that he would think of Doc as "the best longneck there ever was". What really pisses me off is that he says Doc is the only hero he ever met---huh? Has he completely forgotten about his mom? Oh, and Grandpa did save him from the quicksand in 2.