Here’s video of Mills tripping over Mejri’s outstretched leg. If you want to call it an accident you have to explain why a Mavericks teammate pulled him away from heading in Mills’ direction.
Mejri has a bit of a history with San Antonio. As a rookie he yelled at Gregg Popovich after a dunk. The Mavericks were down 20 at the time and Mejri denied saying anything.