Agreed...One wet sneeze happens to all birds every one in a while, I've actually seen my guys do it after getting a drink from their water bowls...So i wouldn't be too alarmed right now, but as stated above you'll want to keep a close-eye on Rambo, and if he continues to sneeze (wet or not at this point, ANY consistent sneezing), or he starts to display any other common signs/symptoms of an Upper-Respiratory Infection such as the sneezing (wet or dry), coughing, open-mouth breathing, wheezing sounds when he breathes, any discharge at all actually coming out of his nostrils, or if his appetite slows-down or he stops eating all together, or if he becomes lethargic/isn't playing or acting/moving around normally, or if he starts sleeping more than usual or during the daytime, then that's when you need to get him to your Avian Vet ASAP...But not for an isolated sneeze or two...
Also, I know you take tremendous care of your flock Amsterdam, but just as an FYI, some birds are actually more prone to being effected by the dust that accumulates very quickly in the bottom of their cages from dried droppings, seed-shells, bits of pellets and other food, etc., so if you haven't cleaned out Rambo's cage this week yet then I would go ahead and at least dump the paper in the bottom and put fresh paper/liners in the bottom just to make sure there isn't any dust bothering him...Also, watch his eyes to make sure that there is no discharge coming from either of them or if they are at all watery or runny, as Conjunctivitis (eye infection) commonly goes along with an Upper-Respiratory infection...But my guess is that it was just a sneeze, probably from him just drinking his water too quickly or eating something and getting it up there, just like we do on a regular basis...
***By the way Amsterdam, I wanted to say how happy I am that you've decided to come back to the Community and that you've started posing on a regular-basis again...We missed you buddy! Thanks again for all you've done and continue to do for birds!