My Chinese water dragon just drooled?

I have never seen mine drool. Did he just finish eating? When mine eat, I notice their mouths are real wet with saliva versus when they have not eaten. Could he have had a water droplet on him from swimming or drinking before you handled him? Maybe it shook or dripped off when he jumped. Or if you just fed him, sometimes they do not eat the entire bug and some bits of the bug (sometimes the guts) will stick to the sides of their mouth and they will fling it off when they shake their heads or it could even fall. Unless he is lethargic or blowing bubbles from his nose or gaping his mouth and has stringy white saliva, I would not be too concerned at the moment based on your question. Keep an eye on his behaviors and also make sure that there is no loose particles or small objects in the tank that he could eat. Keep an eye on the tank too for any regurgitated food if this happened and you had not fed him...more just to take precautions since you are concerned. If his behavior deteriorates then he will need to see a vet, but if he stays alert and active and eating and nothing else has changed, it was probably water or left over food stuck to his face. :)