Correction: the DetNews reports today that it was a hip holster. You won't find exposed triggers there, either--at least if the holster is designed for the gun being holstered.
Hint; you won't have an exposed trigger in a
So what really happened? I don't know, but the top possibilities are that (a) the officer was using a holster that did not fit his gun or (b) the gun wasn't in the holster after all. I hope that someday journalists start to ask the relevant questions in as obvious a "hush-up" as this.