Here we can see the style of weaving more clearly. As you can see, a different technique other than the "three over, three under" is used to make the sides of the basket. This technique is the tboeung, or diamond shape, which is very compatible with the "three over, three under" style.
Basket Making, photograph 14 of 21, from Cambodian Traditional Crafts and Religious Ceremonies.
View the Basket Making group of photographs in order on the Internet Archive,
https://archive.org/details/CambodianBasketMaking.