This one always got me (including this time lol). Tension is 100N. If we pretend that one side is a wall, it's pulling with the same force as the other side, which is 100N. Net force is 0, but the tension must be 100N. Hence, the entire system is static.
A simpler way to view it is to remove the scale and pretend it's a 100N object attached to a wall by a string. Tension is easy to visualize as 100N in that case.