They were probably exaggerating when they said that David was king of the land. They used this question to imply that David was a powerful enemy and Achish should not let him stay there. AT: "You know that this is David, who is as dangerous as the king of the land" (See: [[rc://en/ta/man/translate/figs-hyperbole]] and [[rc://en/ta/man/translate/figs-rquestion]] and [[rc://en/ta/man/translate/figs-explicit]])
This rhetorical question can be translated as a statement. AT: "You know that when the people of the land were dancing, they sang to each other about him, 'Saul ... thousands.'" (See: [[rc://en/ta/man/translate/figs-rquestion]])