Gerald Wallace stayed home and digested news that he said he never saw coming. The veteran swingman then remained in Alabama for nearly the entire offseason before coming here in recent weeks to join members of the Celtics the team to which he had been traded. Wallace formerly of the Brooklyn Nets said he had no idea he’d be included in the blockbuster deal with the Celtics until he saw it on the television screen this summer. “You kind of sit down and look at yourself and wonder what happened” Wallace said at media day Monday. Because Wallace stayed home even missing an introductory news conference because of a prior commitment observers wondered if he was unhappy.