The documentation for git status under “Changed Tracked Entries” appears to explain what R100 means:
<X><score>The rename or copy score (denoting the percentage
of similarity between the source and target of the
move or copy). For example “R100” or “C75”.
So, putting this together with what you cited above, the files you are seeing with R100 status mean that they were moved, and that Git found a 100% match between that file and some other previously named file.
Here is a link to a good @torek answer, which described the physics of how Git tracks content.