I don’t think this is correct. A player does not have to wait for a stoppage to get a drink. They typically do, for obvious reasons, but if a player goes to the touch line during play and someone hands him a bottle to drink from, he’s done nothing wrong. GKS do this.
I do agree with you that no player should be running around with a water bottle, and the R should stop it. And I would stop play if necessary to get the bottle off the field. (But I can’t think of a reason in Law that the restart would be anything other than a DB.)
But that is different from what you do I’d the player did have a water bottle, took a shot, and scored. If play wasn’t stopped before the goal because the R wanted the bottle off the field, I don’t think there is a basis in Law to to disallow the goal.