Actually, I have seen that use case of this before but not with this one. The cost of cup of coffee suits the payment of LN but with this you're right that this is one good example of the use for LN/micro transactions.
But why is it that art work costs not that much? looking at the picture of the painting, I think it costs more.
It's definitely worth more. And in time will probably become an expensive collectible. It's the fact that it was so cheap that got the publicity. And the publicity is worth a lot more to the artist than the 100s or 1000s he could have got for it.
Great marketing!