The app that is now the Element Android app co-existed with the old Riot app for over a year as "RiotX". The rebrand and app changeover were timed together, so

The app that is now the Element Android app co-existed with the old Riot app for over a year as "RiotX". The rebrand and app changeover were timed together, so they renamed the RiotX app to the Element app and replaced the old Riot app with it in one go.