The crowd was following Jesus, but they were not His followers. There is a difference. The crowd followed Jesus up a mountain because they had seen Him heal the sick. They followed Jesus with the hopes that He would fulfill all their earthly desires and expectations. They had heard of a coming Messiah and they looked to Jesus with hope. They had earthly needs and they were looking for earthly solutions.
On the mountaintop, Jesus fed them and their belief in Jesus only increased. However, their belief was still centered on earthly expectations. They decided to take Jesus and make Him their king and they were not willing to accept no as His answer. Because of this, Jesus left them. John does not tell us, but I believe Jesus must have been very sad at their failure to lift their eyes from the Earth to the heavens. They were unwilling to see beyond the flesh and view the spirit. They would not look beyond the present and get a glimpse of eternity.
Even though Jesus left them, they did not stop following Him. When they could not find Him, they went searching for Him. They had not given up on their hope, but they had also not recognized that their hope was limited and misplaced. They searched Him out and found Him on the other side of the lake. Instead of being concerned with why He had left them, their first question was about how He had left them. They were still focused on earthly matters.
This is not just ancient history; it is still happening today. There are people who use Christianity as a substitute for being a follower of Jesus. They are Christians because of earthly and fleshly hope. A person may become a Christian to keep their Christian spouse happy. Another person wants the appearance of morality that religion gives them. Some want to please their Christian parents, and for others it is just business. Know this: “Following Christianity is not the same as following Christ.”