I think most people, including the announcers, overestimated exactly how tight that armbar was. Royce had Matt's trapped leg pretty stretched out, and was pushing Matt's free leg with his (Royce's) free right arm. Matt was pretty much flat on the ground.
Matt was using mostly arm strength, as his midsection was pretty much taken out of the equation by Royce's defense, to apply the hold. That's why you didn't see Royce appear to be in any pain, because he wasn't.