It wasn't Barrett Jones who contained Montgomery in that game, it was definitely Kouandjio. Except for one play where Cyrus seemed to not realize he'd have the help of a back chipping on Montgomery's outside shoulder. Montgomery took advantage of the tangle by spinning back to the inside.
Kouandjio looked great to me and I'm sure he'll be a high quality tackle prospect. But it wasn't just Cyrus that got the better of Sam that day. Michael Williams the tight end did as well. As did pulling guards, or guards when they had Montgomery in straight one on one when Sam lined up at DT.
Hey a bad day can be a bad day, no big deal. But I studied a lot of Sam Montgomery in 2011 and came away equally frustrated and underwhelmed.