You’re confusing two very different things. One is Oracle being careful with the provenance of IP that they let allow into their copyrighted codebase. That’s prudent in the face of real legal uncertainty over the issue. The other is

  > technically such a model should abide by the licence of the inputs, hence all models would probably be GPL

so whether a the weights file of a machine learning model itself can “be” GPL as a result of including GPL content in its training corpus.

That question is a category error because machine learning weights are not copyrightable at all, being mere lists of numbers and facts, the result of a statistical process and not a human creative hand, very much ineligible for copyright protection. They would be protected by trade secret law only, like the coke recipe.

So the GPL, which operates entirely within the domain of copyright law, cannot possibly virally spread from a licensed source code file to a machine learning model which trained on it. That would be a cross species jump. Certainly there could be other legal consequences but in no universe is someone going to jump out and yell gotcha and force OpenAI to personally hand deliver the newly GPLed weights for their frontier model to RMS.