First, I took that 5.9 number from ESPN's football page where they featured Johnson. I didn't watch that game and had no clue he did really well until I looked at ESPN this morning.
Regardless, 4.9 and 107 yards is nothing to sneeze at. Clearly, he runs well and still has tread on the tires.
In the last few games the top rusher against the Browns, by the way, has gained 45 yards, 89 yards, 90 yards, 148 yards, 62 yards, 69 yards, 74 yards, 67 yards, 76 yards.
So, Johnson got more yards against the Browns than all but one runner in the last 10 Browns games.
In fact, Cedric Benson got 67 yards against the Browns the last time the Bengals played them.