That is a massively misleading way to frame it. Hydro is well known as one of the cheapest sources of energy period. The problem being if you happen to have a river of energy. Bundling hydro (and natural gas!) into “renewables” to claim that all renewables lower grid prices (when most people take it to mean solar and wind are impractical) is misleading.
They have graphs for both renewables with hydro and renewables without hydro, the effect is there for both. They also have a separate gas graph too.
But, hydro and gas pairing really well with solar and wind is an actual thing that helps lower energy costs so I don't see why that should be totally ignored.
