It probably was originally windflower's intellectual property (though he has no proof), but he gave it to the 58e for use (I am going to assume free of charge).
He gave his consent for them to use it for the purpose of a thread header.
They are using it for its intended purpose, and were given consent by its original maker to use it as theirs. So, its the 58e's now.
You cant just give someone something, consent to them having/using it, then revoke consent and call it theft. That is not how it works.
Thanks, now kindly fuck off.