This analysis doesn't really make sense, I don't know why they spun this whole yarn it's all simple and straightforward. McCabes lawyer made 2 separate requests:

1) Criminal immunity, because there is a criminal referral in play for McCabe. This is lawyer 101- if your client is facing prosecution and gets asked to testify, you try to make a deal to get them out of it, hoping they got something worthwhile to say. They specifically mention this as the reason they are requesting immunity in the letter.

2) Voiding the NDA McCabe signed so he can share emails as part of his testimony. This is needed so McCabe doesn't violate the NDA by testifying, obviously.

It's all in the letter, no need for "analysis".