He seems remarkably sanguine about the whole thing. He seems to think Greece only imports iPhones and other luxuries. In reality they import about a third of their food, they import electricity, oil, virtually all medicines. He mentions those are "cheap" but that's because the pharma industry was treating them as a charity case for the last six months.

Where I do agree is that Greece cannot radically increase exports simply by switching to their own currency and printing a lot of it. People aren't going to suddenly double their consumption of cheese if Greece halves their prices.

Your link simplifies to an extreme, hand-waving away all the difficult parts of implementing the plan (e.g. how to keep the banks open, how to keep the government functioning, what the response would be of the IMF and ECB, how to prevent capital from immediately fleeing en masse, whether Greece actually has capacity to print and distribute drachmas, etc.). Its suggested approach might or might not work out, but it definitely would not be any kind of smooth ride.

Perhaps he was just overly optimistic in the wake of the referendum No vote. His prediction – “it’s likely the institutions will seek a quick compromise to avoid serious damage to themselves and the Euro” – turned out to be fairly inaccurate. Instead they refused to compromise and in fact made even stronger demands than they had before.