It's sad that you're all thinking drug cheat as soon as a great performance happens. I'm not having a go at any of you because it was also my first thought as he crossed the line. Sad sign of the times especially for cycling which is already very tainted.
The problem is that you can have
great rides, and
extraordinary rides, and it's when you get a performance which falls into the latter camp which, unfortunately, sets the alarm bells ringing. I hate feeling that way - I adore cycling as a sport, but when you recall the Festina affair of the late 90s, sucked in by the lies spouted by the likes of Lance Armstrong (I defended him to the hilt back in the day ten years later, citing his "points" like his different cadence, his use of old fashioned gear shifters to save grams of weight, him rebuilding his muscle structure after his chemotherapy to make him a better cyclist, etc) or that by Brailsford who claimed that Team Sky was going to the cleanest team in the sport with a zero tolerance approach when they obviously weren't ... cycling still hasn't cleaned up it's act: it's just better at hiding it.
I reckon it'll take a couple of decades for cycling to really get its act together, unfortunately.