since the two friends didn't get desert, do you think its an acceptable theory that the desert could've been lobster?
no. depending on what the 'lobster section' is, that would be problematic either way. either the lobster section is meant for lobster customers (lobsters who have come to the restaurant for dinner), in which case lobsters being on the dessert menu would be terrifying to those lobster customers, or, let's say the 'lobster section' is just a section where they serve lobster, then it would seem unlikely that they would serve lobster outside the lobster section, because that would nullify the point of having a lobster section