The attack left one five-year-old girl dead and many people wounded.
Rr Adm Winai said he strongly believed it was the work of a foreign force which had sneaked into the country across the border.
When asked to comment on the attack, he said: "Now you can see what has happened. Who else would do things like this in this area? As I told you, foreign forces are brutal."
On a suggestion that the area was under SEAL intelligence operations, Rr Adm Winai admitted the area was too vast to be fully covered.
He said it was beyond doubt that it was the work of a foreign force. Asked to prove his suspicion, he said: "Thais would not do this to fellow Thais."
Gen Panlop Pinmanee, a prime ministerial adviser, denied a suggestion that the attack on the PDRD gathering in Trat was an overture to his joining the Centre for Maintaining Peace and Order (CMPO). He denied having anything to do with it.
"Soldiers would not do anything like this to the people. We would do this only to armed elements," he said.
"I think people in Thai society are getting more cruel every day. Politics is also heavily manipulated. It is like there is no law. Quite disturbing," the retired general said.
On his joining the CMPO, Gen Panlop said he had not been officially contacted by either Prime Minister Yingluck Shinawatra or CMPO director Chalerm Yubamrung.
Gen Panlop said he still did not know what he could do to help the CMPO. "It may concern tactics to fight an unidentified force doing harm or obstructing police from performing their duties," he said.
He said he had not been in contact with former prime minister Thaksin Shinawatra and any work he does with the CMPO should not have anything to do with him.
"I am not sure if I will be appointed to the CMPO. When this became news, many voiced opposition to me," he said.
On his image of being fond of violence, particularly in the attack on Krue Se Mosque in Pattani on April 28, 2004, he said he had been acquitted by the court after being sued for having overacted in handling the mosque's occupation by a number of Muslim militants. He was deputy director of the Internal Security Operations Command (Isoc) at the time, and the attack resulted in more than 30 people killed.
He said he decided to use force 10 hours after telling the militants to lay down their arms.
"Don't raise this matter to block me. I have cleared myself of it," Gen Panlop said.