Well, no. The law doesn't say 'if you have encrypted information you have to decrypt it'. It says 'if you have encrypted information you have to decrypt it if the police (or someone else with statutory powers to detain your property) require you to'. The HS wasn't required to.
You can't just email someone an encrypted file and key, snap your fingers, and have them be breaking the law. They have to actually refuse to comply with a notice.
Yes, it's a stupid law, but this stunt doesn't actually show anything.