if you want to find out if he is DDR post a pedigree , or reveal his sire and dam. -- ???
Your dog doesn't seem to have any problems. Good open social character . High thresholds (tolerant) . Has good balance , not stimulated easily , and good blocking , so not reactive . Good control and recovery.
quote "However, recently I have observed him tucking his tail between his tails when he encountered few, large dogs in the dog park. He seemed timid or frightened, if I didn't misinterpret him. I'm just wondering if he can grow out of this fear when he grows up. I don't want him aggressive but I want him confident. I don't know how to explain this mixed emotion. I'm very happy to see him friendly, but it is sort of unpleasant to see his tail between his legs. Isn't he a GSD? It contradicts that he has a DDR bloodline. "
how does that contradict anything . You are looking at his reaction as a reflection on your needs , you are embarrassed -- what do you mean isn't he a gsd , and how does that contradict being a DDR dog. Oy . Dog parks , again.
You are lucky to have the dog that you have no matter what lines he is from. Do you have any idea how many people would want to trade places with you. The dog has no problem. You are , however, creating a problem. GSD are not good dog park candidates in the best of times. Focus on the dog doing things with you, for you.