Paul Lydon could be right. The behavior is designed to encourage worms to come to the surface, to make it easier for the geese to find and eat.
From the same Wikipedia page he quoted, entitled Worm Charming:
Worm charming is a behavior also observed in the animal kingdom, especially among birds. The methods used vary; however, tapping earth with feet to generate vibrations is widespread. One common example is the "Seagull dance". The wood turtle also seems to be adapted for worm charming, as it is known to stamp its feet – a behavior that attracts worms to the surface and allows the turtle to prey on them.
This lengthy scientific article is generally focused on the behavior of moles in Florida. However, it makes mention of herring gulls:
Previous investigations have revealed that both wood turtles and herring gulls vibrate the ground to elicit earthworm escapes
The following is from an article discussing that behavior in seagulls, which has also been observed by Paul Lydon. It's interesting and seems pertinent.
According to The Seagull Rain Dance:
Although seagulls will predominately feed on seafood they are also capable of finding sources of food inland for example worms.
Seagulls use this behavior in an attempt to imitate rain.
The seagulls can be observed “dancing” and stamping their feet on grassy areas by raising and lowering each foot in turn. The movement of their feet on the grass causes vibrations which are similar to that created by rain. The vibrations cause worms to move to the surface believing it is raining. This rhythmic beat is repeated, the gulls can then be observed scrutinising the ground waiting for their easy snack to emerge.
The article references work done by Nikolaas Tinbergen, a Dutch ethologist and ornithologist, who earned a Nobel Price for his work in animal behavior. Tinbergen believes four questions that are asked of any animal behaviour can be applied to this observed behaviour of the seagull dance. His belief is that every behavior has a cause, development, evolution and function.
The cause of this “dancing” behaviour could be attributed to periods of rain in which the seagulls can take advantage.
The dance is a learned trick to coax worms to the surface. Earthworms stay underground unless flooded out by rainwater. The vibrations sent into the ground resemble that of rain or an approaching mole.
The seagull dance is a taught behaviour and develops with age. The elder seagulls can be seen teaching young the padding motion on grass. The dance is therefore a learned or possibly inherited behaviour.
Environmental factors play a role in the dance as it is more commonly seen in birds which have to supplement their diet or have moved inland away from the coast. The rain dance is used by other bird species also, for example similar tactics can be observed in thrushes.
While this doesn't specifically mention the bar-headed goose, I think it can apply under sections of the above sources. First, that those bar-headed geese are eating in an inland location, and, second, that the rain dance is used by other species.
As for the bread feeding, the goose seems to stop the dance briefly when the bread comes. Maybe it can't dance and eat bread! Maybe it doesn't need to. That's not something I found in the research.