Before Washington state we had the clear data from the elderly homes in Bergamo Italy where they made the exact same mistake over a month earlier with catastrophic results. Before that we knew from the Wuhan data that CV19 is a highly asymmetric threat and it was critical to protect elderly and immuno-compromised.
The history is still to be written but the U.S. policy choice to go with broad lockdowns of everyone instead of the "focused protection" plan may go down as the worst public health error of modern times. Since they were hit hard and first, Hubei Province and Northern Italy at least have the excuse of no priors. By the time NY got hit any serious analyst knew and many were recommending circling the wagons around the vulnerable.
I have no idea if fault lies with Cuomo personally or someone he delegated this to, but someone in NY seriously fucked up. Hell, in Bergamo prosecutors filed charges against some city/regional administrators for negligent manslaughter (or similar).