Usually the tow release handles are installed on the floor below the pilots left knee. You have to bend forward and reach down with your left hand to pull the handle. If the guy was new, its possible he tried to quickly pull the release when the banner got into the ground and inadvertently banked left into the building as he bent down and reached for the handle.
At the company I used to work for, we went through and installed safety links on all the hook ropes. They were essentially a paperclip type thing made out of 3/16" metal. If the banner ever snagged or hit anything, the clip would bend open and the rope would slide off almost immediately. Way faster than reaching down and pulled the release handle. We used the clips on all our hook ropes but lots of other companies were too cheap to bother with them.
