Which way did he go?

One of the quirks of Cambodian society is occasionally finding numbered sequences going right-to-left instead of the more standard, in the western world, right-to-left. These numbered windows are in a bank in Phnom Penh. It’s curious to me where this numbering might come from since Khmer writes left-to-right and there has never been a colonial power that would have promoted a right-to-left system.