This is not AMP. It’s a feature originally called Chrome Custom Tabs [1], and it’s a faster way to open a webpage than a regular “open URL” intent (that would have to launch the entire browser app) or a custom WebView (which sucks for other reasons). The thing is, this feature takes into account your default browser, so if you set Focus as your system default browser, the custom tabs will launch in Focus, with all the privacy protections it offers.

[1] https://developer.chrome.com/multidevice/android/customtabs