According to this article, you can; it cites the Michigan Penal Code (without taking 2 seconds to note the code section... :hmm
(I bolded the applicable parts here, as I understand it):
(2) A person shall not carry a pistol concealed on or about his or her person, or, whether concealed or otherwise, in a vehicle operated or occupied by the person, except in his or her dwelling house, place of business, or on other land possessed by the person, without a license to carry the pistol as provided by law and if licensed, shall not carry the pistol in a place or manner inconsistent with any restrictions upon such license.
I've seen some speculation he had a license and it lapsed, or didn't have his license with him, or something. Will wait and see... the press release implies they feel it's no big deal, and he's a good guy.