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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.

The back swipe on iOS is per-app, not a global function. I should have clarified. It is different, and a better implementation.

You misread. Parent said the back "button" is a cudgel, not the gesture. Though unfortunately someone at Google decided to give the gesture the same behaviour as the button, so yeah, it is a bit silly on Android.