Id say its potentially had a new engine. Which isn't common for these engines as when the oil pump or pick up goes will cause some serious damage.
The reason that makes me think this is its very very rare to come across a DTM with a warranty.
So either one of 3 things - something has happened to the vehicle mechanically, the previous owner was aware of the issues these vehicles have and wanted to be covered or the owner has just extended the warranty from owning the vehicle from new.
Just another thing to comment is I mean by no means am I trying to put you off but I searched for over 6 months for a DTM. And I have kept track of most of them in the country and I have only ever come across 2 that have had a warranty which is the one you are looking at and one from a gentlemen in derby who was a one owner and had a extended warranty after his standard 60k ran out.
What you can do is ring up any audi dealership in that area and say to them you are in the motion of purchasing the following vehicle if you could know about the history and they will politely tell you. So atleast from that side of things you will have a piece of mind.
Lastly I have seen this vehicle in the flesh. Roughly early last year.
The bits of information I can share is the vehicle was in Audi Bradford for sale it had 55108 miles done. It had a single din radio, it has the phone compartment built into the centre dash the one that hangs off to the left of the centre console, had poor quality nexen tyres, I had a suspect of a boot respray based on the paint colour difference with some paint running as well as the A4 badge was placed on the right side of the vehicle were as it should be on the left. It was owned by "Audi" and then another uk member. So totaling 2 uk owners. Thou when viewing this vehicle it was quite brief as my time was limited and I dont recall looking too much into the engine so I cant verify about the comment I made about a replacement engine.
Thinking about it because it was for sale at Audi it could be that the vehicle still has the "6/12month" sale warranty that Audi offer with approved second hand vehicles.
Hope this information is of some help.