I agree that it was an excellent interview. I think one reason that Mark gave such thoughtful responses was that Shaun Keaveny clearly had listened to and appreciated Tracker. He seemed familiar with all of Mark's solo output and didn't just ask the same tired questions about a Dire Straits reunion. Consider that the song he chose to play was "Laughs and Jokes" instead of the single "Beryl" that every other interviewer played. So Mark sounded like he was having a conversation instead of retreating into his usual stock answers. Even though some of the answers started out in the usual way, he elaborated on them and sounded engaged in the conversation. For instance, when asked about leaving Dire Straits, he talked about it being too big (like we've all heard before), but then added the part about wanting to use a different palette of sounds including fiddles and flutes and upright bass.
Mark seems to clam up when he feels that the interviewer isn't really interested and hasn't listened to his work. But in this case he felt like the interviewer respected him as a musician and songwriter and not just a guitar god. He did seem genuinely touched when he read the letter.