Hansen did his upmost to get him to stay longer; badgering him at every turn before eventually being convinced by his wife that Smith's mind was definitely made up.
The thing about Smith is he puts his heart and soul into the All Blacks; has done for all 208 tests he's been involved. Defence has become his baby, his specialist portfolio, and it means a lot to him.
"He's sitting in there as happy as a wee sandboy with a smile on his face as wide as the Grand Canyon," Hansen said prior to a beaming Smith emerging from the sheds. "When the team does stuff like that he's happy and he takes it very personally when people score against us."
A performance such as this had been a long time coming for Smith. Given how he takes the line being breached, conceding nine tries in two tests against the Wallabies did not please. Last week was much better, just one against Argentina who offered little in attack.
Holding the Boks to zilch, well, you can't ask for anything more. If this is to be Smith's home swansong, what way to go out.
"It's a dream performance to finish on," Smith said. "That's the best forward display I've seen for... ages. Taking apart a team, it was incredible.
"Having a beer in the changing rooms with the boys... the Boks came in as they always do. It's surreal, really, to think it's the last one but the time is right."
Not everything can be measured in stats. The All Blacks made 102 tackles and one would wager at least 90 per cent were brutal as they got the attitude bit right. The edge was there.
Dominant collisions is a polite way of describing the All Blacks approach. More accurately, their forward pack in particular simply smashed the Springboks with line speed and aggression.
"We've been wanting to step up for a while and be more physical. Tonight was the test."
Allister Coetzee has now successively conceded 50 from the All Blacks, following last year's romp in Durban. After 111 years of rivalry, Coetzee stumbled over attempting to avoid calling the Boks' worst defeat to the All Blacks a horror movie.
"One pass goes astray and you're under the poles," the bemused Boks coach said.
Mike Cron and Luke Romano were given credit for doing a number on the Boks lineout - stealing five throws - Smith going as far to label the Crusaders lock innovative and suggesting he will make a good coach.
But the inspiration for this remarkable effort almost certainly came from the man himself; someone who has held the All Blacks clipboard longer than anyone. Someone who is appreciated nowhere more than in this team.
"His story is a lot bigger than just tonight," Hansen said. "He's been a wonderful servant to New Zealand rugby. He's still got some games to go but for him to go out tonight the way he did is only fitting. He's a great man."
