The headline looks wrong, but it actually isn't.
The article specifies:
- Total capacity: 2.1GWh
- Peak output: 1.2GW
- Ramp up time: a few milliseconds
That's what the "within milliseconds" in the title refers to.
Every power generator has a ramp up time. Think the time it takes to start the engine in a diesel generator, until it spins up and is able to output peak power.
Nuclear reactors can hare ramp-up times of hours, in some conditions even days.
This thing here can go from zero to peak output within almost no time, which makes it perfect to balance the sometimes erratic and unpredictable generation fluctuations of renewable energy production.
For comparison, coal or gas power generators usually have large flywheels that, once spinning, react almost instantly to power fluctuations in the network by converting their motion to electricity or the other way round. If these coal or gas generators aren't running, they can't be used to balance the fluctuations in the network, so battery solutions like the one in OP are required to actively manage the network stability.