You left out the part where PG wrote that Altman had already been doing two jobs for several years ("For several years he was running both YC and OpenAI").
OpenAI the non-profit was partly funded by YC or at least affiliated with "YC Research." So it is still odd for them to find out about the quasi-conversion to for-profit like that.
CEO isn’t that kind of job. I don’t have any love for Altman but this reasoning doesn’t fly. You can be CEO of multiple companies at once, and apparently he had been for some time.