I would like to have more technical knowledge to understand it better but as far as I know when a miner finds a block he can decide to include the transactions he wants, that's why sometimes you see transactions below 1 sats/vByte or much lower than the average fees at that moment, because they are from the same mining pool consolidating and things like that.
Yes you are correct.
But the fact that they have been able to draw that image in the block I don't understand it very well either, and it has been expensive for them, right?
Yeah but since they mined the block, they also get all the fees from those transactions i.e. it's as if they didn't spend any money on tx fees to create this image.