While these sorts of mixups aren't unheard of in the mammalverse, "feral confusion" is slightly more common among dinosaurs.

You can see why Luke thought the ceratosaur was actually a horse*. He was feral-shaped, he wasn't really wearing clothes, and his tail pouches kind of resembled saddlebags.

...come to think of it, all those things apply equally to Luke, don't they? Maybe the difference is that Luke wears a hat. As you know, you're never naked as long as you have a hat.

But come on! The cerato was standing in front of the stables! Those markings on his tail... they could have represented a horse brand (though Luke had difficulty recalling if he'd ever heard of a "Double Diamond Ranch"). If the fella didn't want people thinking he had an owner then he should have said howdy when Luke sauntered over to help himself to whatever unattended property resided in those pouches.

However taciturn he may be, Silco is a reasonable dinosaur. He'll give Luke one chance to put those bills back where he found them before he decides to have velociraptor for lunch.

Artwork by  tanukibomb, featuring his ceratosaurus Silco!

---

* Unsurprisingly a "horse" in the dinoverse is any dumb animal you can ride. Actually, I'm starting to think that these dinosaurs originally learned English from a trove of western dime novels that fell out of a strange portal. Whatever happened to their culture, it definitely involved a massive violation of the Prime Directive.