Is all the metadata really in place such that CBS' and other networks' streams are able to be labeled as sourced from public access? I don't know, but my assumption is that it isn't, and that large media companies wouldn't bother to use it even if it's technically feasible.

Given the lack of such metadata on the streams which typically have protected content, the system taking these down probably just looks at similarity of content to streams which are proprietary and silences them "to be safe".