They use AES, but a pretty custom key derivation scheme to get to the AES keys for a specific game given the game's metadata and pre shared root keys installed on the switch at manufacturing time. Yuzu implements that key derivation scheme so that you don't have to track down per game version keys.
A browser does not have the code to decrypt a switch ROM.
It sounds like even then, you'd have to agree to (or read) an EULA to know that this is some magical thing. It is certainly possible to implement something without ever doing either.
It's soft; like a lot of legal concepts, there isn't a black and white test.
At the end of the day it's what can be proven to a jury.
In this case for instance, I don't think there's a decent legal strategy for Yuzu wrt "we didn't know the encryption on switch ROMs was a 1201 protected device".
A browser does not have the code to decrypt a switch ROM.