It's not, but you shouldn't take my word on it. For a supposedly science focused crowd, most people here on HN don't know what they're talking about when it comes to diet. Programmers in general tend to be overweight and unhealthy.

I need special diet to get a six pack (naturally high body fat), but I can do half-marathon, kickbox etc.

It is very possible to be a healthy meat eater but in general vegetarians have lower incidences of common ailments that decrease lifespan in western populations like cancer and heart disease.

Here's a relevant meta-analysis: https://www.karger.com/article/fulltext/337301

And how is chicken not meat ?

No red meat, which is the real meat. In many countries you can call yourself a vegetarian and still eat chicken :-)

Most kinds of preserved meat (bacon, sausages) are very unhealthy. Other kinds have lots of artery clogging fat. Grilled meat can also be cancerous.

It is for me. My stomach doesn't like it, I actually enjoy it a lot :(. I do eat fish,chicken.