I don't see how it's a shock that stock shelves would be empty due to a no deal Brexit. The article points out correctly that supply for goods will be cut short given that their previous trading practice is gone. This will be a short term issue of course, as eventually retailers would find out alternative sources, however this short term issue can spill over and become a chronic problem if not controlled properly.
A sudden drop in supply of good will spike prices, if retailers manage to find another sources then the prices would drop back to their previous levels, however if they don't manage to do so effectively it could could cause some long term dangerous inflation which with an uncontrolled brexit can combine with rising unemployment if investment and capital is pulled out of the country. This could be very dangerous for the British economy because they rely so heavily on imports and cutting it short could very much likely cause a major crisis.
Another problem will be whether Britain will be trading purely on WTO terms or will strike trade deals for its different sectors. Under WTO terms all of its farming and fishing sectors is extremely vulnerable to foreign markets which were previously protected by the EU's CAP.
