Yes, I saw this superb footage of yours. I also guessed the 2 pigeons standing on the pier were also very tolerant to the Anafi buzzing sound ;o)
I agree with you, when you say the Anafi is more tolerant. I think it does not ‘shout and beep’ singing the ‘no way’ song. But the fact is there is a soft iron effect on car roofs and hoods, as there is a soft iron effect on the pier where you did this video.
Not all bridges (that are a collection of concrete with metallic framework with some wires that conduct both high voltages for power supplies and phone lines) nor piers or cars will present the same amount of magnetic field distortion.
In a recent thread for Anafi in FaceBook (I’ll try to make a link here), a guy took off his Anafi from the roof of his car and remarked it drifted uncontrollably just after take-off and had hit a rock and felt.
A lower amount of inboard sensors are also a good option to limit the effects of hard iron and soft iron effects on a drone (Parrot vs DJI).
My cheap tool now is the hand compass (a few € ... or a few £ for sussexors) and I quickly use it when I arrive on the take-off site.
Could you also (if you decide to go back to this pier) measure the variations of the magnetic field as you walk from your car park to the very end of the pier ?
On the roof of my car, I measured around 50° in less than one meter distance.
My theory is the more °/m you get at take off level, the more difficulties you induce to the calculator of the flight board and its estimator algorithm. The risk for drifting increase in this situation.