Plagiarism at worst, spam at best. I'm not sure why they wanted to pretend like they drew it (merit, post count, buy offers) but none of the reasons I can think of are good.
If I have to guess why he did it, my guess would be merit fishing. But as you said, I see no legit reason why would someone claim ownership of painting which is not his, and even made topic about it. We see everyone of us copy images from other websites or image sharing sites but once we add I / my / me to create an illusion that we are the owner of the image then we are trying to get an unfair advantages.
Yep, that's the issue here, he claimed not only once, but three more times after his opening post that painting is his own work. He has the chance to confess and explain that he just took picture from someone else but instead he went on with it.Thank you very much for the tips! I put something like 2 weeks of work in it! How do I participate in the art contests?
I didn't make this artpiece to make money 
. I think I'm gonna put it in my room or in the living room. Thanks for the words!
. I think I'm gonna put it in my room or in the living room. Thanks for the words!Thanks. I may sell it later. I did a bit of thinking and afterall, it may be worth it to sell my artwork. I could make decent profit I guess.
There are no such rules about it, so I think bitcoinermatt will getaway with it very easily which is sad of course.
If admins confirm that's the official stance on cases like this, so be it. I just wanted clarification since report is still unhandled, so I don't waste my own and admins time reporting if I stumble upon similar case in the future.