This once again represents a sentence which omits a lot of important details.

This happened in an experimental setting, not an actual production setting. It was a net positive energy output when ONLY accounting for the energy input of the actual lasers, not when accounting for the mechanisms which fired the lasers (which had an energy efficiency of about 1%, although this efficiency could be higher if they used more advanced laser generator/whatnots). It was generated in a way that in no way resembles what current attempts at a production ready, maintainable, fusion reactor look like (tokamaks), and was instead, as stated before, essentially a design meant for experiments where fusion occurred (basically by shooting a pellet of fusion material into the central focus of a bunch of powerful lasers).

The LLNL is, and always has been, a experimental laboratory meant for primarily nuclear weapons testing and maintenance, and as such, have the ability to test nuclear fusion (via this inertial confinement setup), as fusion occurs in thermonuclear bombs, of which the US certainly has many in its stockpile.

This test, while a big "milestone", is the equivalent of building a specialized fuel efficient vehicle which gets 500 miles to the gallon by sacrificing almost everything that makes a car a car, and then equating that as to say that every car on the road will be getting 500 miles to the gallon any day now. When in fact, the only thing achieved was the ability to say that we've made a car get 500 miles to the gallon.

3 whole energy for the low cost of 300 energies!