Android had the back button since the beginnings. They added an option a few years back to hide the usual three buttons at the bottom of the screen and to enable an ios-like navigation with a swipe up for home, etc. That made a swipe from the left or right edge recognized by the OS trigger a back button. That is quite different from the app itself recognizing an in-process swipe left, showing the underlying screen you would be brought to. Though some android apps do support this as well.