The original commenter’s (OC’s) point has nothing to do with renewables’ reliability.

It is entirely to do with generation vs demand. Grid operators could ask other generators like coal, nuclear, hydro, etc. plants to curtail so inverter-based renewables can export power, but that’s not likely because those producers can’t ramp generation up and down as easily.

Grid stability is a problem when you have overcrowding of generation without enough demand on given feeders. This is moreso an issue with the utilities anyways and how they plan their transmission and substation upgrades.