I heard Thursday April 25 (ANZAC day) is a bar closed day in Chiang Mai, I don't believe it as it should be a weekend for elections, searched on the net but no answers.

Could be. Local elections are scheduled whenever someone decides there should be an election, with no consideration to other events at the time. I don't know if there is an election on 25 April, but it is possible.

Of course there is consideration for other events at the time. They won't hold elections in the middle of major festivals.