I believe he isn't even an alt, but someone who created an account to try earning some money with SmartMixer's referral system by pretending to be them.
Still doesn't change the fact that a tag and warning flag indeed is appropriate.
If we were talking about a type #3 flag against this user, i'd agree with you. But a warning flag is definitely necessary.
We don't want additional user to see this thread and potentially even lose money by using this scam mixer.