I didn't bother watching the video of Geoffrey Mutai, not because I don't respect his running, but because the whole thing is just pointless. Nobody can prove they are clean merely by giving really heartfelt answers about how they don't do drugs. That would seem to be one of the most obvious conclusions from looking at the whole history of doping in sports: people that dope are usually also prepared to lie convincingly about it. For all I know, they may even believe what they are saying. Talking about analyzing their body language as they answer doping-related questions, as if that might strengthen the claim that they are clean, strikes me as a waste of time.
Not to say that I necessarily thing all Kenyans, or Geoffrey Mutai in particular, or any nationality or particular athlete for that matter, are definitely doping. Deciding what is possible and what isn't possible athletically without the use of drugs is virtually impossible at this point - the waters are already too muddied. But trying to use someone's denial of doping as evidence that they don't dope is not going to help matters in the least.