I disagree that this is a textbook chop block, but it is a chop block nonetheless.
If our center is getting held on his way to the 2nd level and the holding DT gets cut by the guard, that is not a chop block.
If our guard gets thrown under the DT who is being blocked high by the center, that is not a chop block.
If our guard accidentally cuts an engaged DT while trying to block the LB, that is a chop block.
It's just like a roughing the kicker call. If you get blocked into the kicker, it's not a penalty. If you dive to block the ball with no intention of hitting the kicker, but accidentally get him in the legs, it is unquestionably a penalty.