it could be, however, even if it was tame, i would think it would still show some sort of reaction when you try to scare it away. Wether it tries to fight back, run away, or play, it would do something. Distemper or rabies will make them not think straight including lack of reaction. It honestly could be anything, I would just personally play it safe unless im sure that its ok.
I can't say I'm familiar with rabies or distemper thankfully. Distemper is reasonably rare here thanks for dog vaccinations and we don't have rabies so I was taking another view
I'd be upset if a fox was stealing my girls. We had a dog attack one of our girls and I'm sure that lead to her dying several months later. Hopefully you can catch/kill the fox to save the rest of the flock.