Cadel's sudden new found 'form' should not really be that surpising to Aussies considering the cloud of drug taking/cheating that hangs over so many of their current sports
Actually, Evans started in not too bad form in 2013 at the Tour of Oman, where he came third over all behind Froome and Contador, and was comfortably in front of Nibali who came much lower in the top ten. Not too bad, and surprising considering how much Evans struggled last year with a virus and how little Evans had ridden in the last 10 months due to that virus. In the mountains in Oman Evans wasn't too far off Froome and Contador, even outsprinting and gapping Contador in one stage.
Strade Bianchi Evans went OK as a helper for Greg Van Avermaet.
In Tirreno Addriatico Evans was poor early, and went into training mode (according to Evans) and came well down on the MTF there. He worked hard for Hushovd on one stage though and still looked fine.
Both Evans and TJVG rode the Criterium International. Evans put in a very average TT performanec, and got smoked by team mate TJVG, so TJVG was made leader and Evans worked for TJVG as a domestique in the mountain the next day. I wouldn't be surprised if this was when BMC and Evans agreed to ride the Giro, because Evans changed his schedule from hilly classics + Romandie to Giro Del Trentino.
In Giro del Trentino supposedly Evans rode it in training mode and didn't bother to follow the other GC contenders (Wiggins, Nibali, Santambrogio). Rather, he just rode at a steady pace once he was happy with his efforts, and still comfortably managed a top 10 position, not helped by BMC's poor TTT. Evans also let Santaromita go in the breakaway on a lumpy day (which Santaromita won).
So, yeah, Evans' form wasn't good, but neither was it at all terrible.
I suspect that the Giro was raised as a possibility for Evans long ago due to the limited amount of riding Evans did last year, so it was always a possibility.
Regarding doping, you'd be naive if you didn't suspect Evans. He was briefly on doping power houses Team Telekom, although he rarely got big rides there despite showing his ability there, and he has had some brief contact with infamous doping doctor Ferrari. But I wouldn't say that Evans is cleaner or dirtier than most others in the peloton. Evans is one of the naturally most talented riders going around in the peloton, he has a huge VO2 max
If you're looking at suspicious form, I would politely suggest that you consider a certain Briton who magically turned into a GC winner late in his career. This Briton maintained his peak for over 6 months in 2012, dominating race after race. This was something physioloically unheard of in the cycling world - Evans, and in particular Contador, were known as cyclists who mainained high peaks for most of the year, but even when they won or went well away from their peaks it was clear they weren't at their best. The Briton credited this feat to his "swimming coach". How a swimming coach created world beating cycling training programs in his first year? No idea.