It is easy to see when people teach pups or dogs to pull, just watch anyone that doesn't have much understanding or knowledge and they often have a strangle hold on their pup. Absolutely it is a learned behaviour.
What is interesting is how people with knowledge and ultra aware hands can take any puppy and that pup will never pull on leash.
Also take that person with the knowledge and skill and watch them take a pulling dog and within minutes WITHOUT corrections, have that dog in a loose leash heel with distractions and WITHOUT holding a treat on the end of the dog's nose..........interesting.
To the OP, since this has gotten off topic a little bit, one thing that is important is to not let the pup forge forward, stop them before they get that far out. Bring them back, nicely and then when they are walking on a loose leash (that doesn't mean you hold the leash at the end, loose but able to take up the slack when needed) reward. I don't reward after I have to bring them back to me, but when they are walking nicely.
You have to train yourself to be ultra aware of your leash, one fun and good method is to have a friend or family member hold the other end of the leash. Each play the part of a pulling dog/pup, learn to become aware when the slack of the leash is STARTING to be tightened, not when it is tight. This includes, forward, bearing out and lagging behind.
Good luck and I hope that helps.