"LLMs don't understand what they say, they just try to sound like they do" is a sentence that denotes a good understanding of how AI works, as expected from an "expert on AI". However, it makes a comparison with human intelligence that either assumes we know how it works, or shows a fundamental misunderstanding of how it works. For all we know, either our brain is a mystery (and thus we can't really state whether an AI "understands" anything, since we can't even define what that means), or, as research on neurobiology seems to indicate, it's just large-scale deep learning, with more ad-hockery for evolutionary stuff, and two orders of magnitude more energy-efficient.