What he sold circumvented the technology protection measures which is covered under the DMCA. This is substantially different to reading and writing generic media.

See 28 in the original complaint: https://regmedia.co.uk/2024/07/02/modded_hardware_complaint....

Also 29c:

In order to achieve this, a MIG Switch circumvents Nintendo’s TPMs by tricking the Nintendo Switch console into treating unauthorized, pirated copies of Nintendo Switch games as authorized, official Nintendo Switch game cartridges.

The idiotic thing is he kept doing this even after a cease and desist.