spoilers:end of spoilers
It's a rewrite. Continuity wise, Keaton is presented as a sort of continuation of Batfleck, like a weird recast. What Batfleck was doing at the beginning of the movie (try to help Barry to get his dad out of jail) get a pay off with BatKeaton at the end, like they were the same character the whole time. Keaton arrives driving the same Batfleck's car he had at the beginning of the movie. I think it's the same car from BvS.
Batgirl establish BatKeaton was the DCEU BM all along in the intro scene, it's a flashback with young Barbara, like a decade in the past, and her dad (Simmons) helps BatKeaton with criminals. As the director said they mix Snyder's and Burton's continuities.
Batfleck is somehow lost elsewhere and need Barry's help to be rescued. From what was described he does appear to be using Lex's tech to communicating with Barry. There's the Lexcorp logo behind him. Maybe Jesse Eisenberg will join him, lol.
General audience will get an headache like us DC readers, lol. Welcome to the club!