The 's' is for 'static' version of the explanation of the name of sbin is not actually supported by any 20th century Unix doco. The books on AT&T Unix System 5 (before which, things were in /etc) that actually give an explanation for sbin all say system binaries, or system administration commands; and none of them says anything about linkage.
The 'static link' story came from Linux people years afterwards. Here's Ian McCloghrie correcting this misconception in a Linux discussion back in 1993:
* https://groups.google.com/g/comp.os.linux.development/c/EKzL...
I pointed out the origins of sbin some years ago.
* https://lists.debian.org/debian-user/2019/02/msg00041.html