I get your point, but there were 4 righteous people that were found.
There was Lot, his wife and two daughters. They were the only people in the entire city who were righteous and God saw to it they left before the city was demolished.
But after departing the city, Lots wife looked back in hesitation and regret and she became a pillar of salt.
Lot wasn’t a native of Sodom, although his wife was. The men of Sodom even recognized Lot as an outsider (Genesis 19:9).
Also, the righteousness of Lot’s daughters was shaky at best, given how Moab and Benammi were conceived.