Kilg%re wasn't destroyed in the last film. With the trailer heavily implying that he made it back to Earth by using Cyborg as a Trojan horse.
Team RWBY have the looks and powers altered by exposure to prolonged stay in the DC Universe.
The RWBY timeline of the movie is post Volume 9. They are in Vacuo after their adventure in the Ever After
The movie comes out on Halloween. Which is Ruby Rose's birthday.
DC Earth has slower time-flow than Remnant. While only a short time has past since they left Remnant, three whole seasons have past in RWBY.