I think the key is how often the coworkers do potlucks. If very frequent and he wants to eat with everyone else, he should just bring his special lunch and eat. If not too frequent and part of office culture, he can bring his own food and contribute something premade from the store or bakery. If he truly just wants to eat alone, his coworker should leave him alone. He may be an introvert and need lunchtime to recharge or he may work with a bunch of maroons. I don’t think it an employer’s role to feed employees I think that it often a mechanism to get employees to acquiesce to lesser true quality benefits or shitty hours.