Maybe you are right, but the local content has been always without ads, and the generic description should be related to both, live TV and own files. It would be a non-sense to add ads to stream a local content that you can easily stream with any dlna server etc.

I think it could be a bug and I would report it. In the Pass description one of the function is the option to skip ads on local content https://www.plex.tv/plex-pass/#modal-plex-pass-features