So, that spot at the top of the door frame where there are 4 screw holes is where the standard pneumatic door closer would have gone, you can even see the mounting bracket in the link provided and how it matches. If there was one installed on this door, there would be some screw holes in the top of the door. If not, then this door was replaced with this different style of closer that I have also never seen before.

I'm not exactly sure if the sliding bar that's on there now is supposed to provide some spring force, it looks like it's just for guidance and there is supposed to be a pneumatic cylinder mounted there as well, but I could be wrong.