Jesus gave teachings related to future events all the time, without clarifying the details or significance of those events.
A good example of that has to do with his Death and Resurrection; the disciples did not get it at all. He dropped clues, and tried to prepare them, but their minds and hearts weren't fully capable of taking it all in. That's why Thomas was such a doubter. He had no idea what Jesus really meant about His Resurrection, let alone that it could or would happen.
When Jesus talks in John 6, he's not giving a full picture, because what he's talking about is only possible in the Resurrection, which they already don't understand. Couple that with the fact that this teaching defies everything we think possible, or can possibly begin to understand about God, and the God-Man Jesus Christ, The Messiah and Lamb of God, then you can see, He couldn't possibly go there, lest they think He was crazier than they were already tempted to think He was.
It was merely a test and a provocation to the imagination that God can exceed any human preconceptions about reality and possibility — So . . .
- Will you trust him, and believe Jesus is God?
That is what He was (implying/asking).