Would there be any benefit in speaking to us main TA about it? Just thinking they must have a handover period at the beginning of lunch and also, if she is brilliant, she would be able to advise the relief TA on the best language to use if he appears to be rude. That might be the quickest way to make the situation better in the short term.
That said, I would be pushing for her to have some ASD awareness training anyway, as without the necessary understanding she will be unable to make appropriate judgements regarding the right way to handle any situations that may arise. Our ASD Inclusion team run free courses for school staff, so it might be worth asking if they do something similar in your area.
My ds hates being told he's rude, it really upsets him, but he can handle - 'I know you didn't mean to be rude, but some people may think that's a rude thing to say - how about saying X instead?'.
As Catsdontcare said, I would also send in a note making it clear what the rules are for eating/leaving food from his lunch box.
I would also make sure you are keeping a diary of everything he tells you and if nothing changes, yes, I would approach the Head and ask either for her to be trained for a for a suitably qualified TA to replace her.