Is my dog a genius or just normal?

As a proud owner of a two year old terrier cross (terror?), I am compiling a list of words our dog understands. This is my first dog so I never realised how smart they are.We avoided puppy school and hate the idea of yelling at your dog to obey commands.

Langly's vocabulary so far:
dog, cat, maggy (magpie), bird, possum, outside, park, shops, car, train (he loves it when we take him to town on the train), up (onto the couch command), duckie/duck, meat, ready (for a walk), walk, go, move (off the bed), kitchen (go round to the kitchen door), postie, bedtime, mummy, daddy, Maisie (daughter), Rohan (boyfriend), cheese, treat, bone (these last three will send him running from anywhere).