When Picard asks if some kind of cloning could be the cause of the two Rikers, Crusher responds: "No, there's no sign of genetic drift." But genetic drift is an entirely different phenomenon related to allele frequencies within a population, and not cloning. What Crusher meant, probably, is DNA degradation.
In one scene on the planet, Riker's duplicate is lying under a table fixing something and Riker is sitting in a chair talking to him. There are two camera angles used. In one angle when the duplicate is talking and a body double is sitting in the chair he is facing directly towards the table but in the other camera angle where you can only see Riker, the chair is at an angle facing towards where his duplicate is lying on the floor.
Shouldn't Thomas Riker also have recieved a promotion to Lieutenant Commander for valor? When we see him later on DS9's "Defiant," he still only a Lieutenant.
Riker: I was thinking... we should probably let Dad know what's
Thomas Riker: (wry) I'm sure he'll be thrilled to hear there are two of us now.
Riker: Any requests tonight?
Troi: Night Bird.
Riker: (pretending he didn't hear her) Anyone?
Troi: Night Bird!
Riker: (he shoots her a "why are you doing this to me?" look) Ladies and Gentlemen... Night Bird.
Beverly: What was that all about?
Troi: (with mischievous smile) Will's been trying to get this piece right for ten years now. He's never made it through the solo.
An early idea by Jeri Taylor had Commander Riker dying while saving his duplicate's life (that's why his duplicate is wearing an operations uniform, he was to take Data's place as operations officer and Data was to be promoted to first officer). Michael Piller hated the idea and ordered it to be trashed.