I think that whether he can do this or not, it is almost certainly not magic, and will have a physiological basis.
Let's see if I can give this a shot-
We can essentially categorise Chang's abilities under three headings - novel physics/biology; paranormal/magic; trickery.
In this case you've more or less asked which category we can put Chang into, coming from a scientific angle. Now, science does not deal with certainties. It deals with logical, internal consistency and confidence inspired by the weight of evidence. So while it's impossible to dismiss with absolute certainty any one category, it is possible to suspend two of them until new evidence arises.
Everything Chang does can be demonstrated as trickery. In other words, his actions can be replicated and therefore explained using sleight of hand, misdirection and plain old foolery.
Novel physics and biology might also explain it. However, this explanation would demand far more observations to remain viable. For instance, why is it that whenever similar situations (involving chi) are tested, the abilities disappear? Sure, Chang could be the real deal. But there is currently no reason to suspect so.
As for paranormal explanations, these can be discounted from the start since we've stipulated we're discussing this from a scientific perspective. Magic has a habit of evaporating the moment it's brought into the presence of logic and reason.
In short, we know trickery exists. We have ample evidence of it. On testing phenomena that has been explained previously using chi, it is consistently found that deceit or misperception is responsible. We can induce that in the absence of any other information, this case is no different.
Is that the final word? Most certainly not. However, for the discussion to progress, evidence that cannot be explained by the 'trickery' hypothesis must arise. Otherwise it is the most useful explanation.
Athon