How is Long John Silver able to hide his disappointment about the map (and his real intentions) so easily?

Silver is being taken exactly where he wants to go. If he were to let on too early, he might not attain his purpose. Thus, he is patiently purposeful.

Silver is been treated how he should. If they all had given him the map they all would have been in a serious trouble. Thus, he patiently waits for the right time when he could get his hand on the treasure map.