That experiment effectively stored a NEGATIVE amount of data in Mimblewimble transactions. In order to locate each 2.5 bytes of data, the program for extracting it needs to know the ID of every kernel in which data was stored, and their correct order. The data extracting program [1] uses 70 bytes of source code to locate each 2.5 bytes of data.

This shows the huge challenge of storing data on a Mimblewimble chain that destroys all ordering information of all outputs and kernels in a block.

[1] https://github.com/NicolasFlamel1/MimbleWimble-Coin-Arbitrary-Data-Storage/blob/master/main.py