> I'd say that's because we don't understand what we mean by "understand".

I'll have a stab at it. The idea of LLMs 'understanding' maths is that, once having been trained on a set of maths-related material, the LLM will be able to generalise to solve other maths problems that it hasn't encountered before. If an LLM sees all the multiplication tables up to 10x10, and then is correctly able to compute 23x31, we might surmise that it 'understands' multiplication - i.e. that it has built some generalised internal representation of what multiplication is, rather than just memorising all possible answers. Obviously we don't expect generalisation from a Pi Zero without specifically being coded for it, because it's a fixed function piece of hardware.

Personally I think this is highly unlikely given that maths and natural language are very different things, and being good at the latter does not bear any relationship to being good at the former (just ask anyone who struggles with maths - plenty of people do!). Not to mention that it's also much easier to test for understanding of maths because there is (usually!) a single correct answer regardless of how convoluted the problem - compared to natural language where imitation and understanding are much more difficult to tell apart.