You are quoting the WHO and then say 'no citation is provided'. The WHO is the source. They are well equipped to research these kind of questions and it is part of their job to issue recommendations and rules about these kind of things.
So receiving a package from China is safe, source the WHO. On the other hand, travelling to Wuhan in person is currently not recommended, source also the WHO.
As a commentor noted, this answer assumes that the statement is actually from the WHO and not a fake. This is the case, see this WHO site.