Actually, the headline isn't wrong, you just read it wrong.

The article specifies:

• 2.1 GWh total storage capacity
• 1.2 GW peak output
• can ramp up to that peak output within milliseconds

Every power source has a ramp up time. Ramping up e.g. a nuclear reactor can take hours, so if demand fluctuates it takes long for it to spin up.

This one here can ramp up almost instantly to cover for fluctuations in the network, especially those caused by the unpredictable nature of renewable power generators.