Like you, I am quite surprised by those attorneys' actions. However, they provided Zimmerman with limited legal advice that may have not addressed any potential legal claims against him; he did not retain them. As far as we know, they made no representations to any court as his legal representatives. Thus, any lawyer-client relationship did not exist.
It's not necessary for them to make any representations or provide any advice to anybody to establish the relationship. If they got any part of Zimmerman's story from him, they're covered.
