We currently make around 1 TW of photovoltaic cells per year, globally. The proposal here is to launch that much to space every 9 hours, complete with attached computers, continuously, from the moon.
edit: Also, this would capture a very trivial percentage of the Sun's power. A few trillionths per year.
He thought SETI listening to space radio waves was dumb, so made essentially a satirical paper saying we should look for heat instead, because "an advanced civilization would be using these Shells to capture all star energy, so we could only see the heat"
The "dyson sphere" was a made up and entirely unfounded claim, without justification.
He was throwing shade.