I wouldn't worry about explaining your MCAT score. A 34 is perfectly fine for Pitt and none of your individual scores are too low. Looking at your MDApps, your application looks pretty solid. If you can, emphasize your trip to Honduras and your research experience in your interview. Service and research are very important to Pitt (although it IS possible to get in without research!).
As for Pitt's average MCAT...I'm not sure. Somewhere around 33-34 I would bet.
Good luck at your interview!
P.S. I highly suggest especially not trying to explain your MCAT score to your student interviewer...it'll probably come across as you being someone who is a potential gunner/someone who cares too much about a few points. I'm sure you're not like that and you're just worried because the interview season makes everyone crazy--just remember, you were good enough to get the interview. Now impress them with your awesome experiences and wonderful personality. If you woo them in the interview, I doubt they'll spend much time looking at your stats.
👍
EDIT: I hope what I wrote above makes sense. We just had a renal exam this morning (yes, on a Saturday...this was the first and hopefully last time) so I'm sleep deprived and brain dead. But I know a lot about pee.