The back page or forward page action mode triggers when you start scrolling when you can’t, and stays locked until you stop scrolling or you navigate to another page.
In Safari and Chrome, you won’t get the back/forward page action until you release the fingers from the trackpad. This way the user can peek forward or backward and see if there’s anymore content horizontally. If the user decided to go back a page, then can just release the fingers, and if they want to stay in the page after peeking they can swipe in the other direction and release the fingers.
I think this implementation is correct, since this is a gracious way to let users surf the web without the need of a keyboard.