Yep you are wrong, but that is okay. There is no contract in place between the Storm and Broncos, ergo, Melbourne could not pursue a cause of action for breach of contract against Brisbane. If there is a clause that prevents Donaghy speaking to potential suitors and he does so, they have a contractual cause of action against him in which as I noted they would probably seek injunctive relief.
Tripp however said the the Storm would take action against the Broncos. If they can't take action for breach of contract, their only other option is for a tort claim based on inducing a breach of contract.
Re the nature of the clause, as I said who knows, however, a non-disclosure/confidential information clause is a completely different beast to a clause that would prevent a CEO interviewing for a prospective position or talking to a prospective employer. That is more in the nature of a non-compete clause.