He said he hoped the release of the memo would cause a Special Council to be appointed. How would that not be material? It shows he planned to interfere.
The lie about "the tweet gave me confidence my story could be corroborated" is immaterial, because whther true or not, Comey admitted exactly what you say. The reason he leaked was to cause a special counsel. If special counsel amounts to interference, then he leaked in order to cause interference. He admits it. Lying about getting confidence on account of a tweet doesn;t change the fact that he leaked with the purpose of triggering the appointment of a special counsel.
The plan to trigger the appointment doesn't IN FACT rise or fall on the tweet. It's a totally superfluous ornament on his story.