So unlike X-Men: Days of Future Past (well, technically that was a mid-credits scene), X-Men: Apocalypse and Deadpool, Logan won’t be throwing an extra scene in one the names of everyone involved with the production have scrolled by.
Some guesses that come to my mind are a special prologue or even some kind of short film unconnected to the main Logan story.
Combined with the Collider update, it’s reasonable to assume that this information is legitimate rather than Mangold lying to keep fans in the dark.
Remember when J.J. Abrams denied that Benedict Cumberbatch was playing Khan in Star Trek Into Darkness?