I suspect the author of the (wonderful) book linked above would suggest that 100% of the pictures would be recognizable as a _picture of a tree_ -- a form which we all learn by age 5 but which does not actually correspond to a physical tree much, if at all.
We falter when we try to draw something that we haven't learned the "correct" pictogram for, because our mental concept of the thing is completely divorced from the appearance of the thing. Most adults can just about draw a chair isometric projection, because they learned how to draw a cube. That crude model of perspective usually falls apart when they try to draw a dog - they know that it's supposed to have four legs, but they can't work out where to put them. You end up with a drawing like this:
https://ellenhenderson.files.wordpress.com/2011/11/dog_new1....
That's because the idea is vague in most people's mind. The don't really care (and they shouldn't need to of course). Ask a bike engineering to draw it, and they will be pretty accurate. However, the people whose idea is vague doesn't know it's vague, which is interesting, and I guess that's the point of the article.
In fact, this translates to much more than drawings, but for all facets of any complexity. You often hear people claim that a particular problem is easy, "just" do X!