That just means that you are not required to recall conceptual content specific to planes. However, it doesn't mean that it is ruled out from the "application" side of the syllabus.
It is possible for an exam question to guide you into doing a vectors question on planes by derivation. For example, given vectors parallel and perpendicular to the plane, they may ask you to derive the Cartesian equation of a plane. Technically, you are just using tools you already know within the syllabus (i.e. the dot product) and just applying it to an unseen problem. However, they cannot ask you to quote the equation of a plane upfront, because that is not explicitly in the syllabus.
Another example is repeated factors in partial fractions. Technically, it is not in syllabus but that never stopped it occasionally appearing in the HSC exams. This is because the exam question must tell you the structure of the partial fractions for repeated factors and you need to be guided into deriving it by using tools that are within syllabus. However, you are not expected to recall the structure of partial fractions when there are repeated factors, because that is outside the syllabus.
