I think the way it works, since he has less than 3 years in the league Oakland had exclusive rights to offer him whatever they wanted and his only option would be to accept it or sit out a year. If they didn't make him an offer, he would've become an unrestricted free agent. It really wouldn't make sense for them to offer him anything over the minimum unless they wanted to go ahead and lock him up in a multi-year deal... but there's really no reason to do that this year when they can wait till next.
Next year he'll be a restricted free agent which allows him to get offers from other teams and Oakland gets the chance to match them.