Yes it is. Before when a potential employer saw a cannabis conviction on a criminal records check they would have potentially ignored it because it is no longer a crime. Now they will think that all the previous convictions that should have been struck off have been struck off and any that show will be treated as having had enough merit to have been deliberately missed out.
Well, then he's dumb, because he should at least acknowledge that the conviction date is from before 1996, so who knows what happened?