That company seems to have a grim record - using banners too big for the tug to pull safely perhaps? Even ATC were concerned enough about his RofC to ask if he was OK.
From moment one in that clip it was obvious what the nature of the upcoming accident would be, ridiculous angle of attack and the aircraft wallowing excessively. It may well have been turbulent, but that a-of-a was crazy. Poor guy.
Fully concur with Juan Browne's observations re inexperienced pilots hours building like that, and the wrongness of the 1500hr minimum.
edit. Fascinating link here discussing the technical aspects of banner towing - I had no idea it was so hazardous - or that this ridiculous permanently almost in the stall at full power activity was going on at ultra low level over a densley populated city! I'd naturally assumed this was just off the beach. What is the FAA doing, allowing single engined airrcraft to stooge around over cities at Vst+5 and a few hundred feet where it's unsafe to pickle the banner? It's utter madness!
Poor kid was only 15hrs on type too.