Ptkay, so where is the definition of what exactly a "closed runway" is?
It becomes wise to mark it closed (as has been done half-heartedly) as soon as the risk arises that it can be mistaken for a runway from the air. Academic definitions of when it is a runway by the letter of the law are unhelpful.
Still, since ICAO only regulates permanently closed runways explicitly (which probably fall into the category you call "closed runway"), marking it in this case was not required, since it's only a recommendation and the closure is temporary, and means of informing pilots were apparently in place. (NOTAMS, ATIS, etc.)
That it still happened is an indication, however, that this was not enough and it should have been considered a temporarily closed runway and marked appropriately. In aviation, nobody is served by just saying "these pilots (controllers/technicians/...) were idiots, and shouldn't have done what they did", and consider the case closed.
People do make mistakes, and what we must do is try to ensure that (1) these mistakes become less likely and (2) the consequences of such mistakes have no grave consequences.