Err...it's definitely no secret that cat owners are weird. We just are, and that's how we like it.
Someone, somewhere, was peeling fruit and placed that peeled portion on their cats' head. Thus, beginning the revolution of cats in citrus hats! Please do not confuse the movement with Dr. Seuss's class, "Cat in the Hat."
We don't know why seeing our beloved cats donning silly things on their head pleases us so, it just does.