Also to add to what Ouberos has said, Klaxians and Oresrians are both mentioned in official Elite Dangerous lore, that being Premonition. It was written using lore provided by Frontier and published by Frontier, with the finale of its story being ingame. Naturally, it's still a secret to the general population in-universe which is why you won't see it spelled out on GalNet, which like the Codex is also an in-universe source of information.
However, the behavior of the Thargoids we see and the timeline of events does appear to back up the theory that we are currently seeing Oresrians. Klaxians would be far more indiscriminate whereas in all cases, the behavior of the Oresrians seems mostly reactive and controlled. Furthermore, there are some inconsistencies between what we see and the Guardian's description of the Thargoids, leading me to believe that those logs are evidence of the Klaxians. One GalNet article from the time even had a quote along the lines of "If the Thargoids adopt the same tactics as with the Guardians, their next move will be to start aggressively mining mineral resources. There is no evidence this has yet begun, however".
It never did happen, either. If there is no Oresrian/Klaxian split, Frontier would have no reason to add that quote to GalNet. Its purpose from the writer's perspective is clear - to highlight that there are differences between what the Guardians saw and what we see.
You use words like "clear" and talk about the Oresrians being in an official book, and while they are, the context is important, isn't it in the book as a "story" or "rumour" someone is telling?
It possible a lot of the speculations that've been made by folks are correct, or close to correct.
I'm just pointing out that they are still speculations (based on evidence, yes, but still)