Probably a corruption of the fact that the protocol to get HDMI out of the Switch is a proprietary alt-mode, which is why standard docks and USB-C to HDMI adapters don't work. But USB-PD chargers are very much intended to work.
The docks that do work generally reversed-engineered the proprietary protocol, and some have damaged Switches because they got details wrong.
The protocol to get video-out isn’t proprietary, just rare —they’re using Mobility DisplayPort from the Switch, and converting DP to HDMI in the dock.
Of course, had they used the native HDMI side-channel (which I’m not sure had been finalized at the time), they would have been able to skip this step.
The docks that do work generally reversed-engineered the proprietary protocol, and some have damaged Switches because they got details wrong.