All the other generators in that grid will drive the out-of-sync station like an electric motor at a faster or slower speed until it's synched up. In effect tha

All the other generators in that grid will drive the out-of-sync station like an electric motor at a faster or slower speed until it's synched up. In effect that's what's happening in the article. Unaccounted load is pulling other generators down, making the frequency unexpectedly low. Perhaps they're not using just frequency to coordinate (solar/wind perhaps needs a sidechannel?), and someone on their grid in a politically unstable area is using power without reporting on the side-channel. Hence the frequency drops due to the unaccounted load.