I'm fairly sure that he might still be acting as AC's solicitor. If he is it wouldn't be very prudent of him to comment on the sentence publicly, either positively or negatively. You'll very rarely get Advocates talking openly, or giving snippets, about the clients they have represented. Listen to any interview with Donald Findlay, Paul McBride, etc.
I get the feeling from that interview that he was asked to go on the show to discuss the role of Defence lawyers in the Scottish legal system and not this trial in particular. Note that he says that he did not plan AC's defence personally, and that he was grateful for the Judge clarifying that in the Scottish legal system defence counsel act upon their clients instructions. The incrimination of TM was all on AC, not the Defence counsel. Who knows what advice they gave him behind closed doors.
This case has aroused a lot of attention in Scotland, and it makes sense that he wished to take part in an interview explaining the Scottish legal process. The interviewer in this case did what any good interviewer would do; she tried to pry a little bit of information from him but he seen it coming a mile off and parried it away as tactfully as he could.
Would also like to mention that Advocates in Scotland have a rule called the 'cab rank rule'. Essentially if someone comes to you offering you money to provide a service, you are obliged to take it and perform that service for them. Ethically, McConnachie had no choice but to defend AC. It's not seen as ethical to pick and choose your clients if you are an Advocate, particularly if you are involved in Criminal Defence.