If I understand correctly how descriptorFromMnemonic() works, it might be possible to have created a wallet with the Network.bitcoin network and then call the function to create descriptors which will end up with testnet paths (the 1h in the following derivation: DerivationPath(path: "m/84h/1h/0h/0").
I think this error will probably be caught at the wallet creation point, where the wallet will reject the descriptor as incompatible with the network provided, but have not tested yet.