In the senate you don't have to be blocking anything for it to be a filibuster. In the senate it means any senator can speak for as long as they wish and on any topic they choose until there is cloture.
But unless there is a vote scheduled there's nothing to delay so its not actually a filibuster, which, per my understanding, references only speech that delays cloture and therefore a vote. So if he keeps it uo moinday and delays the vote, THEN it will be a filibuster. Am I wrong on this?
EDIT: I'm in no way trying to diminish what sanders is doing, whether its technically a filibuster or not right now doesnt matter, he is the lone (vocal) voice of reason in the senate