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.
They do have something to vote on. They got a final offer, an ulitmatum (that Merkel had the audacity to call "a very generous offer" even though she knew fully well that Syriza didn't have the political mandate to sign it), and that's what they'll vote on.
It seems obvious that the germans are shouting the loudest because they have the most to lose on a Grexit. I don't know that the greek goverment has a responsibility to keep propping up the dax at the cost of their own economy that has already shrunk a lot because of 'austerity measures'.
The argument that "you're in debt so you should shrink your economy so that we can keep expanding ours" might make sense to a moneylender, but it shouldn't be what the EU project is all about.
I'll almost certainly lose a shitload of money when the stockmarket opens tomorrow, but i don't think that Syriza had the repsonsibility to stop that from happening.