The thing is he was under contract as the Bills HC until the very moment he opts out. He was still under contract during those 3 days, unless there was specific language in his contract saying he could contact potential suitors. And it's certainly tampering if you lure a coach from another team that was under contract, especially for a lateral move.
Let's pray that the Jets offer him the job, otherwise the case is much weaker. It indeed would be ironic if we received their 1st rounder when Doug quit for wasting away our 1st rounder. However, this is Buffalo sports, so it will never happen.