Well, that could be true about that moment if viewed along with his disposition during the phone call from Sollozzo. He tells Sonny not to lose his famous temper. Sonny then immediately acknowleges that that is his flaw by the look of resignation on his face. Of course, he then reverts to the old Sonny by grabbing Clemenza. So, yes, he may have looked at the chair and internally acknowleged that he could never be the man his father was. I think though that by Michael sitting in his father's chair FFC sent a signal that Michael just did not acknowlege what that chair represented and he was using it purely as a utilitarian device - a place to sit.