Woderick:
Thank you for solving the mystery in advance. Good to escape the 757s long-fuselage rear-end whiplash in turbulence, too. It only remains to wonder how they ensure that the number of non-diners is a number divisible by 6 .....
Pan Am used to do a similar thing years ago (1970s) with a "Thrift Class" at the back of 707s on California to Hawaii, with normal complimentary meals in the main Y cabin but "Meals available for purchase" in Thrift Class.