It certainly is a "very strange approach". And a very stupid approach. Mainly for two reasons:
1) The timing is stupid. The deadline has been known for quite some time. Several EU finance ministers (including Schäuble) suggested a referendum weeks or even months ago. Yet the Greek government waited until the very last minute, then announced a referendum for after the deadline had already passed. They bluffed like the amateurs they are and the rest of the EU called.
2) There is no agreement to sign regardless of the outcome. The referendum as a whole is a farce because there's nothing to vote on. Greece pulled out before any agreement was reached. Nobody knows what voting for the Euro even means at this point. And if the Greek people vote for the Euro, their government is no longer in any position to demand concessions and essentially has to sign whatever the EMU wants.
Basically, if the Greek government wanted to do a proper referendum, they would have agreed on a proposal and held a referendum in late May or early June. Not five days after the deadline passes with nothing to vote on.