[evilduck]

It was at the bottom of the hill. One can imagine a more dense or solid layer sitting on top of a looser layer of soil or sediment beneath it, plus the road acts to hold it all in place like a suture. As the land slide from above pushes downwards into the lower layer, the firmer layer above will move upwards until it breaks.

It's unusual, but hardly something that boggles the mind or deserves the headline provided.

[sandworm101]

Or creating the road removed support or, more likely imho, made changes to water movements that eventually undermined the structures uphill.