I did the trip back in February on a non-o marriage. They wanted to see an onward flight and I had to fan out and count 20,000 baht in front of the boss before I stamped out. I paid 1000 baht for a boat over and back for two people, not including visa stamp fees on the Myanmar side.
Most likely a refugee that never naturalized before committing and getting convicted of a felony. Many Cambodians were deported under such circumstances.