I think he's talking about nameplate capacity vs. capacity adjusted for capacity factor.
Nameplate capacity - The power the system generates at full rated capability.
Capacity factor - Actual production divided by nameplate capacity averaged over time. https://en.wikipedia.org/wiki/...
Nuclear stations usually have 80-90% capacity factor as do most other "baseload" plants including coal
Natural gas plants often run intentionally at lower capacity factor since they're usually built specifically for peaking. In the US, that's around 42%
PV Solar is usually only 13-20% (13-15% in MA, 19% in Arizona)
Concentrated solar power often has a lot of "inertia" in the plant along with built-in storage, so apparently CSP in California achieves a 33% capacity factor
Wind is 20-40%
Hydro varies widely since many countries intentionally overbuild nameplate capacity in order to use a hydro dam for energy storage. (I believe Norway's hydro stations operate at a pretty low capacity factor, but this is partly because Norway acts as Denmark's "battery" and is the sole reason Denmark can achieve around 20% grid penetration of wind/solar.)
So if the installations of solar nameplate capacity matched new coal nameplate capacity installations, in terms of actual contribution to the grid, solar is only contributing 20-30% of what the new coal/nuke/whatever plants are contributing. Another way of thinking about it is that you need MUCH more solar nameplate capacity along with a vast improvement in energy storage in order to match a baseload plant such as a nuclear station.
Also note that this is new installations - most gas/coal plants have already been built, and when renovated/modernized they don't count as "new".