It's not at all ambiguous, it states it exactly how it is.
well maybe it is just me, but i still think as a "documentation" (specially the BIP) it could have been written in a much clearer way by using a slightly different terminology. for instance it doesn't mention "standardness" anywhere instead uses the term "default policy" which i interpret as meaning "consensus rule" not "standard rule".
The differentiation between consensus rules and policies is widely-known, or I have presumed that this was the case. Is it not?