I see a couple of things -

First off, this is a terrier puppy. Terriers are, well, terriers. They have minds of their own and are stubborn.

Second off, this is just a baby. I have a 2 year old pom that I won't let off a leash outside. Why? He isn't 100% on his recall. Period. He is GREAT on a leash but it is the distractions that can get him killed.

So - until you have 100% recalls in contained areas, you are going to need to keep him on a leash. And I wouldn't count on that for a few months yet.