When a coach gets asked if he's staying put he is now in a no-win situation. No matter what he says it will be picked apart and every work critiqued.
He can go the Roy Williams/Dana Altman route and try to placate the fan base by saying he wants to retire there. Then he gets hammered when he leaves.
He can turn to coach-speak, "I'm currently the coach at ______ and am happy here." Then everyone says that's just coach-speak and doesn't mean anything.
The next option is the truth, which is the one Marshall took. And for the record he said nothing like "if I get a better offer". The words he chose were "unless I get an unbelievable offer". The only variable is what constitutes an "unbelievable offer" in the minds of Mr. and Mrs. Gregg Marshall.