This actually sounds like the son has a mental health condition, which isn't an official diagnosis and is still under study, but does appear to exist.

Orthorexia nervosa by proxy.

Orthorexia nervosa is an eating disorder in which the person becomes extremely inflexible about eating habits, generally in an obsession with their health. For example, somebody with orthorexia nervosa might refuse to eat anything that is not low fat, or avoid all food coloring, etc.

"By proxy" means you are inflicting these inflexible eating habits on somebody else. Most often this is a child, but it can also happen to spouses and elders. It can range from the quirky (I can only eat candy when my partner isn't around) to the serious.

The fact that he wanted the food cooked and seasoned in a precise way...and the fact that she clearly was not in agreement with him, points to this. It's a form of abuse, in many ways, and he needs therapy.

This isn't about letting people know in advance...it's even possible that the mother saw a rare opportunity to NOT be told "No, there is SALT in that, you can't have it" and was hoping to get away with it.

We really need to get this stuff in the DSM-IV. I've seen it. Heck, I once stayed with somebody who made me sick because No Fat Was To Be Consumed In Their House Or Presence. We...need...fat dangit. Especially as I was struggling with my weight at the time.

As in struggling to keep weight ON.