Singaporean taxi driver returned $1.1 million to Thai couple

Question: On what purpose does this vacationing Thai couple carry such a huge sum of money (S$1.1 million) into Singapore?  Money laundering?

Bangkok Post, 20 Nov 2012
A Singaporean taxi driver has been heralded as a hero after he returned S$1.1 million (26 million baht) in cash to a vacationing Thai couple who had left the money in his cab.
Sia Ka Tian, 70, was shocked to find the money in a black paper bag on the back seat on Monday after he dropped the couple off at a shopping centre.
But when he brought the money to transport company ComfortDelGro's lost-and-found office, his stunned colleagues counted $1.1 million in thousand-dollar bills.
The Thai couple reported the loss to the transport company and Mr Sia was waiting for them when they arrived to claim the money.
The report did not say what the couple were doing with such a large sum. Full story

Related:
  1. Singapore cabbie returns $900,000 to Thai couple - France24
  2. Sia Ka Tian, Singapore Taxi Driver, Returns $900,000 To Thai Couple - Huffington Post
  3. Singapore cabbie returns lost $900,000 - The Australian 
  4. Best cab driver ever returns lost $900,000, says cash is 'unimportant - MSN Now