Many of his disciples left because they did not understand that his words were of the spirit, as well. Some remained.
That part of the bible is wrong. The entire flesh/blood ritual was completely out of line with all of scripture, and all that we know of Jesus. We have to judge all scripture according to Jesus. Eating human flesh and drinking human blood was never even hinted at. We have a natural aversion to doing such. It is an inherently earthly idea, and has nothing to do with spiritual. Very fleshly, if you will. But why would they write such a thing, since it was so completely out of line with Jesus's personality?
Well, I think the above explains it well. There was always a power struggle among the disciples. Who is closer to Christ? Who will sit at the left and right hand? Who has the authority to cast out demons? Christ was always trying to correct this, but they kept falling back to the old ways of jostling for prestige.
Of course the Jews would walk away when cannibalism was introduced. It was appalling to them. But did Jesus really say that to the crowd, or was it later reported to make the core group look more faithful? I think the second option, because the way Jesus handled the new and shocking teaching was not in line with his teacher personality. He just dumped it on them! He would not have done that, especially knowing the prohibition on eating blood. He would have reasoned with them. He would not have asked them to just take his word for it. He may have said, 'you heard it was written that you must not consume blood, but I say to you . . ."
So looking to Christ, rather than the scriptures, this does not jive. Christ didn't act like that. Lying scribes later added that bit to make themselves look more faithful, and to make it look like they were a part of a convenant that others walked away from. So today, when people decline because they know Christ and know he would not have commanded such a thing, those that go with the lying scribes can compare them to those that walked away in Jesus's day.
No. That doesn't flush with my understanding of Christ, therefore, the bible is wrong on that.