He looks like he is having a good time, but what if he stops right before he is supposed to paint? Does he get his choice, or does he get forced? How would you like it if you woke up and then you were forced to do something. You probably wouldn't like it at all.
It looks fine but I don't think he would do that in the wild. On the other hand It helps the muscles in the trunk.
I think this is a good thing because it is good enrichment and it shows this animal has a lot of natural talent. It also entertains people and himself. It helps build muscle in his trunk too.