There're a lot of differences. Na'vi are twice as tall as humans. Na'vi have long ears, almost like an elf or a cat ear, that can move with muscles, unlike humans. Na'vi have flatter, cat-like noses, whereas you know what a human nose looks like. Na'vi are very long, where compared with humans, they make humans look stubby. Na'vi have a tail, humans don't. Na'vi have blue skin that's bioluminescent in some places, and humans have white or black skin. Na'vi have yellow eyes, humans have green, blue or brown eyes. Na'vi have larger eyes than humans. Na'vi have four digits on one hand, humans have five. Na'vi have a nerual queue that they use with the wildlife on Pandora and each other, humans don't have a queue. Na'vi have stronger bones than humans. Na'vi have little technology, humans have a lot.
If I'm fogetting something, go ahead and add it.
EDIT: Na'vi can only have black hair, humans can have red, brown, black and blonde (natural). Na'vi has stripes, humans don't-
I think he/she was referring to how are they different emotionally, spiritually etc. Not physically since those differences are obvious. So if that is the case then on that level the 2 species are very much alike and I'm guessing Cameron wanted it that way.