From just the headlines, I might have come to the same conclusion. Once I started reading the piece itself, though, the only quote I could find was by the MD of Jamie's Italian, not Jamie the owner. The MD said the price of some of their imported ingredients rose sharply after the value of the Pound dropped against the Euro following the Brexit vote. Well, it has dropped, hasn't it? It dropped following the Brexit vote, didn't it? Probably a coincidence.
The implication that Jamie is just using Brexit as an excuse, and is just bad at business, because his Australian operation also failed, is somewhat reduced once you learn that the Ozzie restaurants were a franchise. He didn't own them and he didn't run them. Although apparently he's thinking of buying them now they're up for sale.
Sorry, but them's the facts... there are too many misleading headlines out there on all sorts of topics and they can't be trusted.