I was playing multiplayer in a vanilla server with a friend. In the image below, this place is supposed to be my 4 chunks mine, during night, monsters spawn there, there's some water I use as 'elevator' in order to go up to the surface. A zombie spawned with full gold armor and went in that water elevator, causing it to be drowned.

In the next day, the drowned got outside the water, it was raining but he was still outside, and due to the helmet it prevented it from burning + the rain.
I went back so I can continue mining this 4 chunks, but the drowned never attacked me or my friend. Instead, it kept wandering around, randomly running into water elevator, when it's there it can attack me if I came closer. Once it's night, the drowned went out and started attacking me.

Below, an image of the drowned that does absolutely nothing, it appears to be staring away even though, I attacked it to see if it can fight back. But not.