I kind of understand where those two women were coming from - hear me out.
While you knew that your dog just wanted to play and was familiar with that body language of Maggie's, they weren't. They didn't know for sure if this meant something else...
That reminds me of about a year ago I walked across the street with my son (then 7) to the mailbox and my new neighbor's dog came running out of their open front door, barking and running right for us. This was a medium sized dog. I grabbed my son, and the woman came running out saying "Oh, she's all bark..." Well, how did I know that? She knew that, but I didn't.
To be honest I'd probably say the same thing at the dog park, but then again I wouldn't go to a dog park because I'd just be scared a big dog would bite Sophie's head off. She doesn't know that she's not the big dog and one of these days I'm worried that another dog will show her just who the big dog is. LOL