I watched the video - just because the paint recovered under heat does not prove the Autoglym theory, it just means that under the application of heat after cleaning, the clear lacquer can behave like a liquid and fill from the surroundings and then reflatten, whether it was scarred on the surface or cratered. That's no bad thing (if you are careful with the heat gun and don't overcook the lacquer).
I've always found that on a well sealed car, as long as you make sure the bird sh!te is fully moistened before you remove it then no etching or marring occurs on the lacquer surface.
He's taken the heatgun solution, thought of one possible explanation and provided it as proof. If he were doing a proper experiment, he should try careful removal of moistened and softened lime that has cooked in the sun, same for lime that has dried in the shade on a cool car - doing it for both a sealed and unsealed surface and see what damage lurks on the lacquer surface under all 4 test conditions.
I certainly wouldn't take his testimony as "proof" that bird lime scarring is unavoidable (but fully reversible), so no need to seal your paintwork to protect it against bird lime.
