Maybe so he could take the Sunderland job. Don't know just a guess. Maybe got a big payout to keep stum. Have no idea, but his autobiography will be worth a read!!
The claim in itself would not have stopped Gus taking another post and he didn't get a payout. It appears Gus probably chose to drop the action on legal advice because he was unlikely to succeed (and/or Sunderland may have made it a condition of his employment offer...).
Also I thought a 'settlement' was reached by which Albion would not seek legal costs from Gus that had been accrued as a result of his claim? If this is the case then it is highly likely the agreement included a confidentiality clause, in which case Gus' book may well be a lot quieter on the subject than you hope.
I'm guessing too mind you.