I can't say for sure if he's natural or not but it is possible. In america they have professional strength coaches in high school and schools have very well equipped gyms. At 19 he could have been training under proper guidance for maybe 5 years (stabbing in the dark, haven't read his history). Include possibly some better than average genetics and athletic ability into the equation, and I don't see why he couldn't be natural.
We've seen what Markos can achieve with guys at PTC in a short time, so imagine if this guy had been training with good coaches for more than a few years.