At the bottom of the stack, the answer is probably either "it fit perfectly in an 88x31 space between some other things on the first page it was used on" or "I drew a rectangle that looked right and didn't bother rounding the numbers".

As it turns out, if you put two horses side by side...

I think the parent refers to that which is a classic one: https://www.physicsforums.com/threads/the-link-between-a-hor...

It's 88x31 GIFs all the way down.