Chernobyl was caused partly by operator error. The expert here has clearly an agenda of his own, if he denies that the testing that caused the accident was made outside the original test specs, ie. the power levels when the test was started were way too low, and the operators responding to the unstable conditions caused by the initial power levels were incorrect and ultimately caused the secondary explosion, which was the main cause for the release of the radioactive materials.
The conjecture about overfilled cooling pools is also totally unconfirmed by any other source, as is the claim that the pools drained after the quake. As far as the official story goes, the pools started draining as there was no active cooling (pumps died, like in the reactors) so the stagnating water evaporated by the heat produced by the spent rods, which makes sense as pools drained by the quake would have caused problems immediately, not after a few days.