It is understood that they believe Jesus can heal the paralyzed man. This can be stated. Alternate translation: "When Jesus perceived that they believed that he could heal the man, he said to him" (See: [[rc://en/ta/man/jit/figs-explicit]])
This is a general word that people used when speaking to a man whose name they did not know. It was not rude, but it also did not show special respect. Some languages might use a word like "friend" or "sir."