You probably triggered off a background conversion process which kept going and popping up warnings when it couldn’t modify the system libraries as it should not. Nothing sinister like you think.
I think the instructions for Ubuntu packages are equivocal. Too much is mentioned about the option to not install the recommended additional packages. I believe it should just present the default, and then at the end mention that if one does not wish to install the recommended additions because one has one’s own arrangements, one can disable that with --no-install-recommends. In the package maintainer’s quest to save user download volume, users who don’t understand the nuances end up without libraries, and then they do multiple downloads and post queries here. The volume of the symbol and footprint libraries is small in the scheme of things.