It's not actually my logic, it's what it says on the page flap of nearly every DC Comics elseworld tale......
I think this film having more in common with the STM films, instead of being a restart, is one of the gripes of the fanboys. It's something to debate, really.....but, I'd be hard pressed to want Singer to only cater the comic fans anyway.
I believe the good word to use could be ADAPTATION. Since, apparently, Elseworld is a dirty, dirty word.......heh.
But.....most films seem to stray from the current regular comics anyway, so to speak. Spider-Man, X-Men.....even those films aren't based on the regular comics.