South America is where it's at

Sean is very interested in South America. We read a book about Venezuela that we got from the library, and in that book Oscar D'Leon was mentioned. I suggested we could look for his music at the library as well, and Sean said, "Let's look on  iTunes." So we found him on iTunes, Sean was very into that music, and we have one of his CDs on order at our local library. He loves snakes, and one of the books is about the Fer-de-lance snake, which lives in parts of South American.
He has been exploring a book about world cultures, and seems to be heavily interested in all things culture, history and geography right now.
This week, I very informally read to him about the history of numbers. One of the pieces of information talks about how the Egyptians alternated from left to right on one line as they wrote numbers, then from right to left on the next, in the same way they would plow their fields. I found it fascinating, because Sean tends to do that as well. Until late in his third year at Montessori he did this, and still sometimes will start to do it.
For a while he also wanted to write right to left instead of left to right, and read the right page first in a book. My mom used to say he would do well to learn the Urdu language, which is written right to left.
While some would likely see this as a problem, I find it interesting and wonder why he would find that to be a natural way of doing it. He used to write his numbers across a page, and when he got to the end, he would just drop down to the end of the second line and start writing backwards, until he reached the end, and then drop down and go left to right again, like this:
1 2 3 4 5 6 7 8 9
15 14 13 12 11 10
16 17 18 19 20
and so on.
He does it the way the rest of us do it now, but he asked for a grid paper one day last week, and said he wanted to write numbers. He began to do it again.  It must still be a way that is comfortable to him...
I'm not worried about it, I just find it interesting.
Has anyone else encountered this with their children, or children in their classrooms?