The laser didn’t generate 2 quadrillion watts like a power plant would generate electricity, but it delivered that much power in an extremely short pulse, like 20 quadrillionths of a second.

That means the energy it delivered was relatively small (a few hundred joules), but because it was delivered in such a tiny time window, the power (which is energy per unit time) was immense.

The laser did produce power, in the form of intense light and heat, over a very small time period. It converted 2 quadrillion watts of electric energy into a very brief laser pulse.