Sure they did. Not so long ago, a lot of people thought that black humans were a different specie, or at least a subspecie.

If anything, humans tend to be more prone to look for differences than assume equality.

They(we?) were more related to each other. I guess that like chimpanzee[1] and bonobos[2], perhaps closer, but my biology knowledge is not strong enough to choose the perfect example.

Note the humans and chimpanzees diverged like 5 million years ago. Neanderthal is very close to us and it's reclassified as it's own specie or as the same specie from time to time.

There is a nice graphic in https://en.wikipedia.org/wiki/Chimpanzee%E2%80%93human_last_... Neanderthal is not in the graphic, but if you want to add it, you should put in near the top left, between us and H. Erectus, probably closer to us.

[1] https://en.wikipedia.org/wiki/Chimpanzee

[2] https://en.wikipedia.org/wiki/Bonobo

Having just seen a comparison of human and Neanderthal skeletons in person, it seems rather far fetched that they couldn’t tell each other were different.

"Same thing" obviously has blurry boundaries. Neanderthals might have seemed to be a different race or the like.

Yeah, and any human can tell that you are not the same thing as me. We can form all sorts of groups… people with dark hair and light hair, skin color, eye color, nose shape, etc. Which differences determine that another person is too ‘other’?

I always recommend one of my favorite essays for this topic: “The categories were made for man, not man for the categories”

https://slatestarcodex.com/2014/11/21/the-categories-were-ma...

You will have to ask them