The Yorkie vs The Dogue De Bordeau

[Macomom]

Hello,

I was wondering if you could help me with better understanding this situation?

I brought my dogs to an off leash dog park in our area. When I got there I noticed there was a lot of small breed dogs, so I introduced myself to the group of people and asked if they would prefer that I take my large breed dogs to another area. They said no, to join them in the park so I did.
My Dogue De Bordeau is 105lbs and 17 mnths or so. He was very intent on playing with a tiny Yorkie. He would go to her, and she would get nervous and be a bit aggressive with him. The dog was fearful so I would call Boswell off the Yorkie and he would leave her alone.
As soon as I called Boswell off, this Yorkie would come over to us. Then the cycle would happen again, and I would call my dog off.
This darn Yorkie, as scared as it seemed, just kept coming back to my dog. The owner said it was scared of large breed dogs.

It was kind of unfortunate because I spent a lot of time telling my dog what to do and what not to do, while the Yorkie had free rein.
Why was this Yorkie so persistent in engaging in a situation which obviously made her fearful?
Cheers,
Joanne