The key word here is material. The ToS statement proscribes not incomplete answers but (knowingly) incomplete material. Just what might sensibly be construed as constituting the latter, in the context of answers to questions on MSE, is open to interpretation. However, an answer that provides a clear guide to tackling the problem posed by the OP, which omits only details that the OP can be expected to supply, can arguably be considered complete, as a guide or hint, albeit incomplete as an answer. An interpretation of "incomplete material" overriding enough to deem incomplete such complete hints would probably also consign almost any reasonably compact answer to the "incomplete" sin bin. Consequently, such an interpretation (whether or not intended) will not be respected.
One might add that explicit proscription of deliberate obviously-bad behaviour on MSE, even when framed accurately enough to not preclude good behaviour, is pointless because (1) few users will read it for a start, (2) it cannot be enforced (except retrospectively, which will happen in any case), and (3) the handful of people who deliberately behave badly will ignore it anyway (in their short-lived presence on the site).