Smit, who switched from hooker to tighthead prop for the Cardiff clash, believes defence is an area in which Wales have greatly improved since Edwards came on board earlier this year.
"Certainly the greatest aspect (of their improvement) is their defence," said Smit, whose side scored 34 points when they last visited the Welsh capital 12 months ago.
"They stopped us from playing the kind of rugby that we want to play. You could see that it was an aspect that they had worked on.
"There was certainly a frustration (for the Boks in attack). A lot of the rugby we prepared for and trained for, we couldn't really enact, so their defence was certainly up on the button."