Earlier quoted context omitted.
/usr is absolutely where user data was. That's what it stands for "users". First when / ran out of space, new programs were put on the other disk /usr in /usr/bin so everyone could assume programs were in /bin except ones that were newly installed so they would be in /usr/bin When /usr ran out of space, a new disk was added as /home and things that were easier to move (user directories) were moved first leaving thing…
/usr stands for Unix System Resources
https://www.bell-labs.com/usr/dmr/www/notes.html
See also, from:
https://www.tldp.org/LDP/Linux-Filesystem-Hierarchy/html/usr...
In the original Unix implementations, /usr was where the home directories of the users were placed (that is to say, /usr/someone was then the directory now known as /home/someone).