What is proper dog park etiquette?

My wife and I got a Corgi puppy a couple of months ago. She’s now nearly 5 months old and she has all her vaccinations so we can take her outside to meet other dogs. We’ve taken her out back behind our house many times now, and when other dogs walk by she gets both really excited and very scared. She’s had some interactions but not many. Yesterday we decided to take her to the local dog park so she can gain experience socializing. The park was totally empty so we just let her off her leash to run around. A little while later a guy showed up with an absolutely massive dog, I think it was a mastiff. It was on a leash but as soon as it saw our dog, it yanked hard and the guy lost control of the leash so it got free and was just careening towards us. Our dog freaked and ran towards us, my wife picked her up but the mastiff was jumping up at us. This dog was taller on its hind legs than us mind you. It wasn’t aggressive but was very jumpy and excited. We tried to have the dogs get used to each other but I think there was just too big a size difference. The owner kept telling his dog to not jump but it didn’t listen. He got the leash eventually and walked away a bit, but soon again the dog wanted to run over and he lost control again. This time it leapt right on top of our dog and she really snarled, which I’ve never heard her do before. I grabbed her but again the mastiff kept jumping up on me.

The guy wasn’t rude on anything but he kept asking about our dog’s age, breed, and wondering if it’ll ever get bigger. The implication to me was that he thought our dog was too small to be at the park.

My question is: what should we expect at the dog park moving forward? Is it appropriate for us to bring a little Corgi there? Should we have her on leash at all times? Was this guy just an irresponsible owner? We’re both very new to this stuff and genuinely just want to make sure we’re not breaking some “unwritten” dog code etiquette. Thanks in advance.