New York’s First Electric Skyscraper Promises Luxury With Lower Emissions | An apartment tower in downtown Brooklyn has ditched fossil fuel heating and appliances
Most electric heat pump hot water heaters have a slow-mode which uses the heat pump, and fills a large tank with hot water, and a fast-mode which uses a resistive heater when the tank runs out. I don't see why this situation is particularly different for larger buildings, except that they need a larger tank and an electrical supply which can deliver the needed wattage.
Cheapo landlord could of course install an undersized unit, as they can with any other key system.
It still amounts to "I'm heating up a big tank of water and supplying it to people on an as-needed basis." The article makes it clear that they're using several to supply the whole building:
Electric water boilers | These provide hot water for the building and are typically more energy efficient than gas boilers, which are common in New York City.
Fair enough. I guess there could be a time when they need resistive to augment that but I'd think with sufficient boiler capacity you could do only heat pump.