First off, I'd be pretty upset at the JR owner for not controlling his dog better. grrr Poor Milo, no wonder he's not confident at the park.
Here's what I did with Yogi. He's my youngest and I would say he's more cautious then shy. We started going to the dog park when he was probably 5 months old. He went with his older sister (Gracie Ruth Queen of the World, Goddess of Retribution-if-you-don't-do-what-I-say
) and his older bigger brother Boo. So he had 2 dogs with him that he knew. He was so overwhelmed for probably 3 months of nearly weekly visits. He didn't want to follow his pack or sniff anything. He just wanted me to hold him - which I rarely did. So he would sit on peoples feet. Not just mine, anyone who was close by and standing still. He felt comfortable with people, knew they'd take care of him and just sat and took it all in. I'd look over and see some poor person with a very perplexed look on their face, look down and there was Yogi sitting on their feet.
After about 3 months he started stepping out a little and smelling things, or following Boo or G for a short distance. As he got more comfortable with all the sights, sounds and activity he'd venture off by himself and maybe even introduce himself to another dog. After about 7 months he was comfortable at the park and would run, bark and play with Boo or G and occasionally a small dog or little puppy that was in there. A few months ago, a small tiff broke out between 2 other dogs and Yogi was burning a trail over to the fight when I hollered at him to stop. Good boy that he is, he did, looked around at me. I asked him, "What do you think you're bringing to that fight, little boy?" He got a very hurt look on his face and said, "aww Momma, Iz nots a wittle boy!" So all this to say, just give Milo some time, try real hard to only pick him up when he's really in danger. Let him work it out for himself those other times. You can separate him from a dog that's bothering him, but try to do it without picking him up and then just walk calmly away. It's ok if he follows, he'll venture out again when he feels secure.