"Optimistic but not obviously unrealistic inputs" include reducing the cost of hohlraums from the million dollar range to 10$ (not even sure if that accounts for the price of the gold itself), a reactor capable of resisting 50 million pulses before needing replacement, and a few others.

It also considers the price of a fusion power plant to be less than that of a fission power plant, based entirely on the observation that it would have less stringent safety requirements.

Overall this article may be right in principle if taken to refer to an arbitrarily far away future (hundreds of years away at least, if ITER and DEMO are to be taken as realistic examples of the pace of improvement of fusion power in general, even if they are MCF instead of ICF).