Vietnam says so here:
Vietnam has released four Cambodian Sea Border Patrol officials arrested in disputed waters and accused of piracy, the Vietnamese coast guard said Friday. The four Cambodians were released late Thursday night on orders from the central Vietnam government, after confirming they were members of Cambodia's border patrol.Background info here.
But a Vietnamese official said the incident at sea on Thursday raises new questions about a series of pirate attacks on Vietnamese fishing boats.
"I think that these Cambodian coast guards were the ones thought to have been pirates who raided many Vietnamese fishing vessels before," said Nguyen Kim Hong, deputy commander of Vietnam's Southern Regional Coast Guard.