I don't think Balz's technique in this video is old school at all. Here is a real "old school" duck tack by Robby Naish from around 1984 at 3.12mins.
Robby changes to switchstance just before he ducks under the sail, then sails backwinded and only then carves upwind to complete the tack. The main difference to Gerdes and most other people's duck tacks is that Robby lets go of the boom completely and literally ducks under the foot of the sail whereas Gerdes throws the sail to windward, mast directly in to the apparent wind and then ducks around the clew, always (nearly) keeping a hand on the boom, more like in a duck gybe. But otherwise Gerdes' and Robby's duck tacks are similar.
Balz on the other hand stays with his foot in the front strap, carves hard upwind and only releases the boom and ducks as he is pointing dead upwind. He comes out of the duck on the new tack and hence there is no sailing backwinded. I have never seen anyone do this on a fin riding a wave or freestyle board.
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