The function called at program startup is named main, which this translation unit defines. No other may therefore define it. Binaries that don't run main are out of the scope of the standard, and so irrelevant to the discussion.
Anyway, as a more general point: your argument is, basically, "the customer is wrong". But the customer is never wrong! Therefore your argument is invalid.
Right, yes, sure, whatever. Since you've evidently got the experience that I apparently lack, you'll know that this point is irrelevant, since the topic at hand is Standard C, and not whatever some random implementation happens to do... so I'm not sure what your point is. But of course perhaps it would be obvious to a more experienced practitioner.
Anyway, as a more general point: your argument is, basically, "the customer is wrong". But the customer is never wrong! Therefore your argument is invalid.