Are Poya days dry days for foreigners too.

Yes the nationwide ban on the sale and public consumption of alcohol on Poya days applies absolutely to everyone including foreign tourists. Bars and restaurants will refuse to serve you. However the law specifically targets public consumption and commercial sales. If you smartly purchased your own beer or arrack the day before you are perfectly legally allowed to consume it entirely privately inside your hotel room or quietly on your private balcony without offending anyone.