The idolatrous ideas of what they thought of the planets came from having eaten the fruit of knowledge, after they ate the fruit, not before.
The tree was called "of knowledge", the plain language attests to that.
Cannibalism arose as a result of "eating" that other knowledge, not before eating it. In fact, Adam and Eve hadn't eaten meat of any type at that time. Nonetheless, it wasn't a physical eating to which that referred, but to "eating" by taking in knowledge leading one astray from the one God, in order to become gods (vainly). To eat such was to receive death because Life can only come from the One God who gave it in the first place. Because they ate Death, God barred the Way to Life.
The opposite Tree was the Tree of Life, and of Himself, Christ said, I am the Life. Christ brought down the Gospel from Heaven as God the Word, and it is that Doctrine which one should "eat" to receive Life. Just as Jeremiah foresaw when he said:
16 Your words were found, and I ate them, And Your word was to me the joy and rejoicing of my heart; For I am called by Your name, O Lord God of hosts. Jeremiah 15