How many years between pictures? He was still a teen when he became well-known. With a few years at such a formative development period along with serious weight training, he could certainly do it naturally.
Looks like he's juicin. Of course he could have just got done lifting weights. Looks like he's been fake-n-bakin too.
Are we sure it's not photoshop'd? A similar picture came out for Bargnani in his second year, and it was a fake.