Here’s a new version of the old ‘synthetic yes or no’ question. This is actually a grammar question. “not recommended” is different than “not required”. “not recommended” infers something negative will happen if you use synthetic, which (aside for the extra money you spend) is not true, no harm will come. Had he said “not required” or “not needed” (for Camrys, at least), he’d have gotten an ‘A’. As is, he gets a ‘C-’.