> eh, there was probably something similar in the trainset that the LLM just had to tweak slightly

Look for examples of mixed image-text generative AIs, and see how they are able to understand visual jokes and memes and explain the source of their humour.

To do that, the AI not only has to recognize and classify the items in the image. It also has to identify the context of the items in the image, and figure out what elements are unusual in that context.

All that process is something that could be only imitated if the training set contained exactly the same meme; as the source of humour will be different for each image. But the AI is capable of doing it even for memes not included in the training set.