You might be confusing this case with a penalty during a "scoring play" as in 10-5-1d,e,f. For a foul by the opponent of the scoring team during a try, FG, or TD, the scoring team would have options for enforcement on the KO.
Notice that safeties are not listed under those special enforcement provisions. Instead, the case is covered in 10-5-4, which mentions no KO yardage.