The Theory: In Logan, we learn that X-23 is part of a secret program, where Xander Rice implanted children with mutant genetic material in the hope of creating his own race of secret weapons.
Well, some fans think that one of the child experiments just might be time-traveling mutant Cable, who travels back from a war-torn future to the timeline of Deadpool 2...for some reason.
Why It Can't Be True: The timeline of the X-Men movies is convoluted enough as it is, and considering that Logan is pretty much a standalone spin-off, Fox may not want to risk tampering with it by retconning certain aspects, no matter how seemingly minor and harmless they might be.
Plus, we didn't see a kid among Laura's friends that even remotely resembled Cable, and if they were going to do this, they'd probably make some sort of Easter egg out of it, no?
But..What If?: Deadpool 2 is clearly going to be incredibly meta, and this would be a fun, playful way to recontextualise Logan without screwing with its bigger picture.
Plus, time travel would be a fairly neat way for Cable to bring X-23 into the fold for the planned X-Force movie in the future, so getting the ball rolling makes a lot of sense.