Asked fellow american about his health insurance in T'land, both of us retired. He said he can get treatment here at hospital, send billing to Medicare USA and get reimbursed.

He did say that this notion was only reported to him by his friend and that he himself had no direct experience. I have never heard of such a thing. I expressed my scepticism but could be mistaken.

Any first hand information on this idea?

Impossible.

Perhaps if he was here on vacation. When I only spent 6 months a year here and was still covered by OHIP in Ontario Canada, I could bill them for hospital expenses in Thailand, and did.

Perhaps he was referring to Tricare for ex-military.

Your skepticism is well founded. Medicare does not apply outside U.S. borders.

http://americansabroad.org/issues/

Medicare

Americans abroad who are eligible for Medicare benefits in the US should be able to sign up without premium penalties for late enrollment upon return to the US.

Executive summary:
Medicare benefits are not available to citizens outside the United States. Premiums are increased for those who sign up later than when first eligible, and some American health insurances require the insured to pay Part B premiums even when living abroad. This encourages citizens to travel back to the US for expensive treatments, which would cost far less in their countries of residence. TheTriCare program available to military personnel overseas has shown the feasibility of extending Medicare coverage abroad.