At the time Smit suggested to referee Stuart Dickinson that it had been a spear tackle but no cards were shown.
Thorn admitted lifting the Springboks captain off the ground before dropping him on his back, an action SANZAR judicial officer Dennis Wheelahan said constituted an act of foul play and was "contrary to good sportsmanship" rather than a dangerous tackle.
Wheelahan imposed a suspension of one week up to and including July 13.
After the hearing at New Zealand Rugby Union headquarters in Wellington, Thorn said he felt he had received a fair hearing.
He added: "I'll be missing the Springboks game and that's very disappointing.
"But the decision has been made and I'll accept that."
Aside from his moment of madness, Thorn - alongside fellow lock Ali Williams - made a huge contribution to Saturday's winning effort in Wellington and his presence will be missed in next weekend's Test in Dunedin.
Thorn has made no secret of the fact he loves to scrum and New Zealand certainly had the edge in that area of the game, although they struggled to get clean ball off their own put-ins at times.
The pair also more than matched their much vaunted opposite numbers Victor Matfield and Bakkies Botha in the line-outs, especially in the first half, with both sides having to adapt to the new Experimental Law Variations where there are no restrictions on numbers.
Williams, playing in his 50th Test, said playing alongside Thorn was a joy.
"I can't speak highly enough about the guy," the lock said. "He does everything he is required to do and more.
"Physically he just loves it. He dominates people. I've got so much respect for him.
"That was a special game for both of us. We were really up to the challenge and the respect you've got to give Victor and Bakkies is huge."
The weather - wet, cold and windy - meant it was always going to be a game that was won up front and so it proved with number eight Jerome Kaino scoring the All Blacks' only try and the remaining points coming from the boot of fly-half Dan Carter.
South Africa's try to Bryan Habana came against the run of play from a turnover inside their own 22, and proved once again what a lethal finisher the wing can be given half a chance.
But there were few chances for the backs to shine and instead, captained by Rodney So'oialo at openside flanker in the absence of the injured Richie McCaw, the All Blacks forwards took the game to their rivals.