I very much relate to dieting as a default stress response, or even as an identity. Like when someone else is doing it they're somehow threatening who you are, or who you were. It makes you want to reassert yourself as "the best dieter," at least until the temporary insanity passes.
The good news is that the more time you spend as the non-dieter/happy eater, the more comfortable and normal that feels. It gets to the point where you feel sorry for dieters, or experience a genuine flash of relief that it's NOT you. A friend texted me a photo of an odd looking brownie the other day and said "fat free." I texted him back a photo of a one of my dark chocolate, peanut buttter buttercream frosted, hunks of Reese's Peanut Butter Cups brownies and said, "not." :-)
Practically speaking though, there's nothing to be done about other people's dieting behavior. I don't try to educate or discourage them, or explain my point of view. I don't ask them to behave differently around me. It's fine if they want to eat zoodles or avoid bread and talk about it nonstop. Good luck to them. Been there, lived that. I wouldn't want to experience it again.