I didn’t know making a painting of a picture was plagiarism. I wouldn’t have thought that.
Even though the medium is different, it's still someone else's work. You need permission at the least.
It's probably not a painting but rather posterizing with photoshop or even a free online service.
He stole the picture, changed the contrast, and substituted colors, and put it out as his own. Takes less than 5 minutes.