Arbitration agreement had sufficient mutuality in the counter-party's agreement to be bound.
Dissent: State law requires that, in order to create an enforceable agreement, both parties to an arbitration agreement must agree to arbitrate claims.
http://media.ca8.uscourts.gov/opndir/18/08/171191P.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.