It's good that the link to the library solved the issue for you.
I'd say it doesn't matter whether root or postgres creates the
symlink. If postgres should normally be the owner of
/usr/local/pqsql/lib directory ... then postgres should have
been able to create that symlink. And it's always safer to have
people do things as a non-root user. I'm guessing that is why Don's
instructions said do it as postgres. Doing it as root won't break
anything.