No clue. I'm assuming that they must receive some sort of data from the ATM operator as part of the transaction. Either way, it was pretty neat that it all worked like it was supposed to without any intervention on my part.

Here's an example of the transaction: http://imgur.com/3L65Lkn

The fee was always 200THB at various ATMs, which on the posting date above (1/4/16), comes out to around $5.54, so the reimbursement was pretty much spot on (going off of this reported conversion rate: http://www.exchangerates.org.uk/USD-...e-history.html).