This shortcut was discovered many years ago by David Wonn, but more recently (Aug. 2020) replicated by Forest.

Forest's original WS lap skip proof of concept
Forest's 0.91 lap TAS
How does this work?
By jumping over the wall further down the track, we can get set our last section to a location that will be more than 1000 units away from the top of the wall that is by the finish line. Because of this, the game will then fall back to finding the closest path marker to the character which happens to be right behind the finish line. If we clip the wall without getting stuck, we can make the game think we are on the other side of the wall, trigger the finish line while falling, and then immediately be done with part of the race. We then jump back over the wall and cross the finish line to immediately finish the lap.
Why are you using Bowser/Wario?
The RTA setup was made using Bowser with the thought that it might be a bit easier to make it back over the wall after the tumble because of his height. One could be made for other characters though.
Why did it take nearly a year for someone to actually do this strat?
Nobody with the ability to work on an RTA viable setup had enough motivation to spend the time making one I guess.
SC lap Ranks
SC lap WR history