The model doing the compression is trained with a human language corpus. Also, this is a generic procedure to feed another model trained on a similar corpus. Therefore, I'd not expect the compressing model to do anything exotic.
Btw., humans are quite good at compressing as well. SMS used to be billed per 128 characters. Also, any slang or technical jargon are attempts at compression. These are how people push the limits of expressivness and contribute to language evolution.