they're doodles (Droedel is dutch for doodle ;) ). They just "happen".
They're mostly made to kill time when commuting to work, or during meetings. Which means most of them are made in the short trip back & forth to work (say 10 minutes for each trip if I have a place to sit), they're coming straight out of a black pen (no erasing) on a scrap of paper, usually A6 - cause that fits in my hand or can quickly be put away during that boring meeting - and yes, second hand paper, so sometimes the backside of the paper I used shines through, or the scan shows the many folds because I put it in a back-pocket. By now I know every curve the metro
First time a twisted kritter got printed (as far as I know).
And nope, not exactly a children's book, it requires a bit more than a few hours to read (and probably some deep thinking).