How long do saved passwords stay on a phone?

When using a website yesterday, an email address and password that was saved 3 years ago, and not used since, appeared when I tried to log in. I thought I had deleted this persons information, and having had 2 new devices since I am confused as to why it has appeared after all this time? When trying to understand it more, it says that saved passwords only appear when recently used. In this instance, this was not the case as I haven’t had contact with the individual for over 3 years. Please someone help me to understand why this would have come up?! Any advice/guidance is incredibly helpful.