So google frontend engineers use dreamweaver as their editor?

They use it ironically. They are hipster devs.

How does some js file rendering some random angular/react DOM for client side tell what editor it was written in, without even being passed to said client, so this extension could tell you?

Or the other way around: how does a file saved with nano differ from a file saved in vscode or dw or atom or <any other editor here>?

@nitwhiz Comments, metas, default JS boilerplate.