It's not not a crisis either, though. Crisis doesn't really have a formal definition, it's just an extreme devaluation. I agree that what's happened so far is not quite yet a "crisis", but it certainly seems like Krugman was attempting to predict that not-this would happen.
That tweet was 2 days ago and the pound has barely moved against the dollar since then. It lost a few cents, but that's hardly a crisis.
It is a crisis when you already have an inflation crisis. People already can’t afford to keep warm this winter. Therefore, the government is capping energy bills, if there is a currency devaluation the government has to borrow more to maintain the cap...