Nobody walks on the sea in Mark. If you want an explanation of how somebody might see somebody else walking on the sea, in bad light after hauling nets for a few hours, then take an introductory psychology course. Or just read the ghost sighting reports that are all over the web.
You mean be seen that way by some of the people we were just discussing, the ones who saw a ghost on the water, now seeing this after being marched up a hill in the desert sun. You have an odd notion of what "instantly" means. This probably took days to make it work, even for a talented perfomance artist like Jesus.
That's in John, about a generation later. In Mark, Jesus and his handsome assistants mime sharing the food you brought with you with your neighbors. People catch on, and everybody eats. Jesus apparently didn't bring any food himself personally, although as you say, the boys did, and thus they had props for the mime.