"The next day, though, Ramirez was merely pleased to see others sharing his one-off doodle. In the anonymous world of 4chan, having other people recognize your contribution felt good."
He clearly didn't have any issue with that, and without any license posted, that was already a violation wasn't it? They shared his work without stating the author and without his permission. Yet he was happy about that, until he smelled some money.
It's like if you would put a basket of candies, some people approach you and try to take it, and you're like "sure, take it, I'm glad you like it". And this keeps on for a while. And then some guy in a suite comes in and takes one candy like so many others. At which point you start running after him shouting "THIEF! He stole my candy!"