Yes, that is an attractive balance of line and form, as you say. The rounded shapes contrast nicely with those straight lines.
Those lines are indeed mysterious and look far too regular to be caused by wear. I did some research and the general idea is that they were indeed caused by wheels. Once there is a bit of a rut, all following wheels will find their way into it and wear it further. I also found this interesting article, which suggest roadworks in a busy main street in Pompeii were as annoying and disruptive as they would be today, especially as paving with cobblestones would be more tedious than modern methods, so they came up with the idea of using molten iron to repair it quicker!
archaeology.org/news/2019/05/15/190515-pompeii-iron-roads/