The ps.1 manpage incorrectly stated that psr field showed the
processor the process was assigned to. However if the assignment
has changed but the process has not run, then the field doesn't
change.
Some digging by @srikard showed it wasn't the processor assigned
but the last one it was run on. The man page now correctly
describes psr in that way.
References:
procps-ng/procps#187