Where do you get your "knowledge" from??? It's bull shit. Even it's a communist regime country, Vietnam allows citizens from 26 countries to enter without a visa and stay for a specified period.
No, it's NOT the truth. The BEST 2 days for Songkran party in Pattaya are on 18th in Naklua and on 19th in the other parts of Pattaya, because it's called "Wan Lai". If you didn't know yet, now you know!