I don't think there are any indications that the Guardians were that similar to us?
They do sound 'mammal like', but had a totally different bone structure. They also favored sign language over speaking.
It also seem implied that they have evolved from a pure carnivore type pack hunter animal.
I'm thinking more wolf than monkey.
They are described as being bipedal, slightly taller than the average human, with two arms, four fingers on each hand. vestigial noses in the middle of their face and two eyes that are similar to human eyes but slightly larger in the front of their heads, small mouth under the nose, they have blood that is exactly like a humans, they eat the same food (although they can also digest meat uncooked). The major differences are more flexible bones, two joints on the elbow and spikes on the forearms and red skin (but it is skin, just as we have, and in different shades of red like we have different skin colours). Those similarities alone are absolutely remarkable on a biological level.
Yes they are described as pack or tribal hunters and nomadic (in their earliest history, but that can also be applied to us too, we didn't settle down until very recently in our evolutionary history), the wolf analogy is great, nice work, although again, we also fit that description. Even if they are more wolf than monkey (we're descended from Apes by the way, not monkeys) that alone would still be an amazingly remarkable discovery, and doesn't preclude that they could be our ancestors.
If we (in the real world) encountered aliens that looked like that our scientists would go nuts over how similar they are to us since it's such a crazily remote possibility that another form of sentient life would evolve all those traits exactly like us (because there are so many options).
Plus, as we've said, Ram Tah also comments on how similar to humans they are right down to the DNA. He says that we could live on their worlds with no problems at all.
Again, it's not a coincidence. They are related to us 100%. Just depends whether they made us (accidentally or deliberately) or we're some offshoot of their descendent. I suspect we're the (descendants of the) Exile colony to be honest. I think the narrative is all going that way. Especially since the first Alien artefact found in the Elite universe by Humans was on Mars in the early space development (and is still kept secret there) but no other artefacts of sentient life were found there, suggesting it was left by a space-faring race, the info is in a tourist beacon around Mars if you want to go look. It's entirely possible that's a Guardian artefact (although it's supposed to be very small, the size of a finger). It could easily be a data stick or something, maybe that's how Ran Tah translated the Guardian data so fast, maybe they already had a lot of data and all he did was run the new scans through the translator. It did seem that the knowledge we collected at the Ruins sites was what was amazing to him, not the fact that the Guardians existed at all.