. So that leaves improved aerodynamics and that is either self generated or moto generated. I'm going with the camp of Moto assist.
Matt Bottrill is obsessed with drag and aero. Friends of mine ride against him (I am not in that league, or even same bit of road!)
As a pure TT cyclist they take it to a different level than triathletes, not having to run afterwards.
He also believes that triathletes should train as if each discipline is separate, using the best know ideas for each. (at least he used to) rather than swim-bike-run
If Tim Don is working with him there is likely significant input/change on this parameter.
I'm confused. You say at first you think his improved aerodynamics is more likely from a moto assist, but then go on to say if he's working with Matt Bottrill there is likely significant change "on this parameter" (you mean aerodynamics I assume). So which is it?
As Fleck points out above, there are other options - how well the athletes are trained early in the season, as well as how well they gauged their effort over the 90km.
It may be he received some moto benefit, but until someone who witnessed him doing so chimes in here, it's a bit presumptuous to assume that was the primary factor. It's not like Tim Don has come from nowhere to beat these guys. (2002 World Duathlon Champion, 2006 World Triathlon Champion, 3rd at the 2014 70.3 World Championship.)