That looks like a pancake box. They’re not rated to support a ceiling fan as far as I know. And the fact that it’s a pancake box probably means there is a joist or something there that would prevent the installation of a proper fan box in that exact location. There is a box made for going over a ceiling joist, if that’s what is above this pancake box.
Here’s an example of one if this sub allows links. There are several different kinds.
Edit: I looked again and the ceiling is built lower where that box is. Idk why they would have used a pancake box in this situation. So my ceiling joist theory is probably wrong in this scenario.
Can you shut off the electricity and remove the box to get a better picture? Just unscrew it and see what is underneath. I couldn’t get your imgur link to load