I think they are basically saying an OS project with a single commercial entity as the maintainer.
So I don’t know—maybe it wasn’t intended this way, but it comes across as very gatekeep-y to me. Like telling people that unless they are already established and famous enough to start a project that has tons of backing from the start, that they can’t “really” be opensource (despite a very real opensource license), meaning you as the little guy should either build your project for free with no hope of ever making a living from it, or else be excluded from the broader opensource community.