Quoting this for you to answer your question since it was an old member account.
Back in the old days, anyone could use an avatar.
His account is from 2011. Before the change, he was using an avatar, so he stayed with it.
Accounts that have registered before the implementation of the merit system are able to still use avatar. Only newly registered accounts are unable to use avatar until they will become full member.
The merit implementation doesn't able to upload an avatar to a member rank