Not any more than this is the "default painting of humans on a genetic level". It's just easy to draw and someone without any drawing experience may stil ldo it easily.
Which was in many ways the original point when developing Odo’s look by Westmore. The unfinished sculpture, like the protohumanoids in TNG. But as the story on DS9 progresses, it’s quite apparent something different is going on with why he looks like that, in universe rather than out of it.
And a stick figure is basic iconography, rather than an attempt at ‘default human’ made in complete ignorance. It’s a developed symbol only. Otherwise the head would be a different shape for a start — not every child starts drawing with stick figures unless taught to do so, and the choice of additional details and the order or style in which they add them is always interesting. (Hair, fingers, face, style of facial representation, secondary sex characteristics, clothes, how the clothes are added, ears… sometimes used as developmental markers.) The same is true when looking at what might be labelled ‘primitive art’ or art history in general. But in all those cases, we are talking about external representation of self, and of a group, rather than what in Odo’s case would be an internal representation — he is his own self portrait, with more control than other people. Why does he choose *that* eye colour, in universe? Why mimic the structures of the eye so closely, when he clearly does not need to? If he can do such small and complex detail, how could Bajoran nose ridges, or Cardassian forehead indentation be beyond him?
Perhaps he chooses his default face precisely because to be Bajoran would be to invite more difficulty from the Cardassians, but he does not wish to be Cardassian either for much the same reason.
Better to be something different from both, and better to hang onto whatever identity he can muster.