It's more of a question of if a specific document is using AMP, the site can be a mix. Just like a site using jquery as an example.

An AMP page can be identified by examining only the first few bytes of the HTML. The `<html>` tag will contain either the `amp` or lighting-bolt emoji attribute, ie: `<html amp>`.

Technically an AMP document must pass AMP Validation to be truly AMP, so there are documents that match the above condition which aren't valid AMP. There are multiple ways to validate. A starting place is https://validator.amp.dev/

If you turn off Javascript the site won’t render for 8 seconds if it’s an AMP.