In fact the community involvement in development as exemplified by GitHub (and SourceForge before that) is to a large extent invention of the same group that started using the term open source (for what is otherwise mostly the same thing as free software).
It is, however, the case that open source under the GPL is a perfectly well-defined concept, as is free software under the MIT license. The terms refer to worldviews about the code and ethical obligations, not to licenses.
Linus cares a great deal, he just doesn’t want to be cornered as an FSF zealot.