As to Lewis himself being clean, again watch the documentary there were only about 2 runners in that era (regularly making the finals) who were clean, the athletes know better than anyone.
Objectively Lewis was a full grown man and out of no where his jaw grew, displacing his teeth and he got braces to fix it as an adult. Jaw growth and braces were indicative of the steroids used at the time in the 80's and was common place with the track stars, who prior to jaw growth had perfect teeth.
Even in modern times in track what gave Russia's state sponsored doping program away was the simple fact that non doped athletes would be doubled over from fatigue at the end of events and the Russians would be smiling not even out of breath, like the article suggests world class is world class and so like I suggest the athletes will simply be in the best position to know when something is out of the norm.
As to Bolt, what makes him special as a sprinter is his size, once thought to be a detriment (like the article says), but he wasn't/isn't a freak, it is more along the lines of self fulfilling prophecy. Take Russia and China for example where they just pluck kids from school who are identified based on certain physical traits and go into state sponsored athletic training camps. Moreover, When you were a certain size you were just over looked by everyone including the coaches and put into different events, now that Bolt has broken the mold, tons of kids more inline with Bolt's body size are/have been identified and given the proper support and coaching, so in the near future we will see more and more sprinters similar to Bolt's measurements. This will inevitably lead to new world records in the short term without the need for genetic modification or peds.