Admittedly this isn't my main area of expertise, but I have done some machine learning/training stuff myself, and the thing you quickly learn is that machine learning models are lazy, cheating bastards who will take any shortcut they can regardless of what you are trying to get them to do. They are forced to get good at what you train them on but that is all the "effort" they'll put in, and if there's something easy they can do to accomplish that task they'll find it and use it. (Or, to be more precise and less anthropomorphizing, simpler and easier approaches will tend to be more successful than complex and fragile ones, so those are the ones that will shake out as the winners as long as they're sufficient to get top scores at the task.)

There's a probably apocryphal (but stuff exactly like this definitely happens) story of early machine learning where the military was trying to train a model to recognize friendly tanks versus enemy tanks, and they were getting fantastic results. They'd train on pictures of the tanks, get really good numbers on the training set, and they were also getting great numbers on the images that they had kept out of the training set, pictures that the model had never seen before. When they went to deploy it, however, the results were crap, worse than garbage. It turns out, the images for all the friendly tanks were taken on an overcast day, and all the images of enemy tanks were in bright sunlight. The model hadn't learned anything about tanks at all, it had learned to identify the weather. That's way easier and it was enough to get high scores in the training, so that's what it settled on.

When humans approach the task of finishing a sentence, they read the words, turn them into abstract concepts in their minds, manipulate and react to those concepts, then put the resulting thoughts back into words that make sense after the previous words. There's no reason to think a computer is incapable of the same thing, but we aren't training them to do that. We're training them on "what's the next word going to be?" and that's it. You can do that by developing intelligence and learning to turn thoughts into words, but if you're just being graded on predicting one word at a time, you can get results that are nearly as good by just developing a mostly statistical model of likely words without any understanding of the underlying concepts. Training for true intelligence would almost certainly require a training process that the model can only succeed at by developing real thoughts and feelings and analytical skills, and we don't have anything like that yet.

It is going to be hard to know when that line gets crossed, but we're definitely not there yet. Text models, when put to the test with questions that require synthesizing abstract ideas together precisely, quickly fall short. They've got the gist of what's going on, in the same way a programmer can get some stuff done by just searching for everything and copy-pasting what they find, but that approach doesn't scale and if they never learn what they're doing, they'll get found out when confronted with something that requires actual understanding. Or, for these models, they'll make something up that sounds right but definitely isn't, because even the basic understanding of "is this a real thing or is it fake" is beyond them, they just "know" that those words are likely and that's what got them through training.