Yes, they walked away because they did NOT understand what Jesus was saying about hiim being the "mana of God".
No, they did not walk away, because Jesus did not present it that way. That was added later. If you come to know Christ, you would know that he never would have taught such a thing. It was completely out of line with all other teachings. Manna from Heaven and the Word and all that fits, but taking it a step further and making it an actual cannibalistic, symbolic ritual is not what Christ was doing. He was using metaphor, and lying scribes came along and changed it, and people that don't look at the entire picture and what Christ was really about, follow them.