Saw this in a newer (2004) condo building. In one unit only, rear bedroom master bathroom basin. It was a double basin vanity, but only one of the basins displayed this.
Supply (from valve to faucet) were steel tubing and the drain was steel. There was a green pateena on the supply pipes and the drain had green and black. The hinges for the door also appeared to be corrosed, but not with rust.
No Chinese drywall (not used around here) and only one of the two basins were affected.