He turned out to be Amnart Choodate, 38, a volunteer with the Kathu District - but his credentials were quickly revoked when officials learned of his activities.
Kuwaiti tourist Fahad Al Mutariy, 57, suffered a broken nose in the pistol-whipping with the .38 outside the Royal Palm Resort at 4.30am.
Khun Amnart also carried 18 bullets, the officers said.
What's still unclear is the motive for the beating but police did say the tourist had not been drinking.
Khun Amnart will face serious charges, including possession of an illegal weapon.