INCORRECT TYRE INSPECTION

I purchased a vehicle privately from an individual and as the seller, he needed to get a roadworthy certificate and a AA Dekra point check done. The roadworthy was perfect and all the checks were fine. The tests were done on 12 December 2014 with 48401km on the clock. I recently took my vehicle (AUDI TT) for its annual service and the vehicle has 50500km on the clock now. To my shock and dismay Audi tell me that the tyres are all completely worn (the words were \you are driving with slicks"). Surely the tyres should not have passed the Dekra test in the first place then? If I was told that the tyres should be replaced"