Could be.
At the risk of "being annoying," I'm still not sure that's true. Ryan Torain was injured for the first three games of the preseason. He didn't practice with the team until August 27th, five days before the preseason finale. Obviously, he didn't suit up and didn't receive a single carry in the preseason until that finale.
Evan Royster, on the other hand, played in the first preseason game for the Redskins. He was healthy for the next two preseasons games, but did not receive a single carry. Ryan Torain dominated carries in the final preseason game, the only one in which he played.
So, what I'm saying is that Torain was never in danger of being cut, and Shanahan's not going to come out and say that. Doing so runs the risk of alienating players who play all preseason and making them believe you gift positions on the 53 man roster. He was the #3 back because he was injured, but Royster's usage (or lack therof) in the preseason makes it pretty apparent that the Redskins had little to no plans for Royster.
Maybe Torain was one of the last players in Shanahan's mind. I'm not sure one way or the other and I don't think it matters much. The reason, if any, was because he had a broken hand and couldn't play or practice.