"Filibuster" isn't even a legal term. It doesn't appear in the Senate rules. It's a colloquial term. So there's no way to decide, as a legal matter, whether what has happened or is happening is accurately called a "filibuster."
But, whatever we call it, if the DemocRATs succeed in blocking Estrada's appointment, they will have successfully set a precedent (actually a further precedent, after Fortas) that, where a party is willing to use all its power, 60 Senate votes are needed for the confirmation of a judge. It's that (further) precedent that we ought to want to stop, and it seems to me a cloture vote is a way to try to stop it.
-PJ