Obviously you can't turn shit into gold in a few hours or even days so his story is obviously exaggerated. However you can literally transform in the space of one (or a few) hour(s). You obviously still need to have that base and muscle to begin with though. I am sure Milos if he posed at the start of the time in the video for a bit would have looked great but pale and soft/flat with no pump he may have looked very different. He used site enhancement which would have an obvious and significant effect. However just loading carbs with insulin and pumping up could have a dramatic effect.
I am nothing special at all even for just a gym rat but that should prove things even more. Meaning if I can do it someone with amazing genetics (muscle shape, volume etc) would have even crazier results. I have looked at myself at times and literally looked like shit (flat and soft) and 2-3 hours later after training I was hard, ripped and veiny and looked like a totally different person. That can be done by solely training and maybe an intra shake of aminos and carbs with some nitric oxide expanders pre/intra workout as well. However if you also add in other booster such as cialis the effect is even greater. Now add in Adenosine Monophosphate (AMP) and you will feel yourself growing (pumping up) after every set and the final fullness and vascularity is insane.
It should go without stating this only works on lean people who already have some vascularity but the changes are crazy. I don't compete but guys who do will know the tan itself can be magical as well. I once tried pro tan for a laugh when lean (should have got pics done) and it was crazy how I looked compared to no tan and that was just the tan (no added pump etc). So combine all these elements with actual site enhancement as well and the short term changes could be dramatic.