It requires sunlight to charge, not to produce electricity. Because liquid salt doesn't cool the moment it goes dark the plant can continue to use it to boil water to spin a turbine for a fair bit of time without sunlight. I believe one implementation only produces power at night, and spends the day collecting heat.
But yes, solar power does require sunlight at some point.

It's kinda moot however, because having now read the original post I was correct to assume they (the doe) was being disingenuous. The heat they seemed to be referring to was "the weather". As in "despite the high temperature, the sun still went down causing solar generation to ebb in a predictable fashion that grid operators were unsurprised by. This is why it's good we forced them to keep 150 year old coal plants burning".