When wearing this outfit, make sure to have a jacket on. In fact, I would always have one on when tucking your shirt, so the proportions of your body (long legs, small torso) are hidden/balanced.
I think he merely wanted to show the trousers without having part of them hidden by a sportscoat. Otherwise +1, tie and spread collar=jacket. Some say spread collar=suit but I don't really care. Pants are nice for chinos, they look substantial.