One of my males does this very slight sometimes enough to be noticeable....when in a calm state, he is very trustworthy, healthy, eats from my hand, anybody know? For communication maybe??
Rocking and swaying are part of a threat display. Some chams do it more than others. He's probably reminding you he's a big tough man. If he were to get more upset you'd see his display escalate with color change, puffing himself up, coiling or lashing his tail, gaping, pushing out his throat, etc.