Why is my rear rack shaped like this? I recently bought a used bike that had a rack attached to it. Until last night I didn't notice this strangely shaped part on one of the sides of the rack (circled in purple in the picture). This isn't on the other side and it isn't on the rack on my other bike or the rack on my roommates bike either. I believe that this piece was partially responsible for the issues I had attaching panniers to my rack.
My question is what is this and what purpose does it serve/why is it a part of my rack?

Edit to add photo of top portion of frame pump holder as well.
I suspect it is one end of a pump holder. It holds one end of a pump. If my suspicion is true, there should be at the other end of the rack something to hold the other end of the pump. You compress the pump against a spring in the pump to attach it to the rack. This works only for pumps having a spring.
Presumably the pump that came with the bike (if it was an accessory sold bundled with the bike) has long ago gone missing. You may not be able to find a replacement pump of exact the same length.