Top left corner of screen showing last application a user was on

I was wondering how often and when does your iPhone display the last application a user was on. Bf sent me a screenshot and his top left corner showed Tinder as his last application he was on. He claims he downloaded it for a friend then says he must have accidentally clicked on the app from recents and that’s why it displayed on his screen. However when I use my phone I seem to have to be on an app for a decent amount of time in order for it to be shown in the top left corner of my screen to go back to. Thanks