Fun fact: the original image was animated by hardware palette rotation. Imagine paint-by-colors where every pixel is a number that translates to a specific color in the palette. Instead of a fixed key where 1=green, 1 is changed over time from green to black to green again, creating the illusion of movement -- the pixels themselves do not change, but the palette does. And there's only 256 numbers to pick from.
It was an extremely efficient hack. The program only had to change 256 bytes instead of hundreds of kilobytes each frame to animate an image. The scary part is that the animations had to be hand-crafted, pixel by pixel.
Funny this one was posted, the creator is probably lurking here somewhere but I made some slight additions to that gif.
This is the OG source though: http://mochipanko.tumblr.com/post/124096842688/ah-pouring-rain-with-the-sun-setting-is-blissful
No, definition of pixel art is that author places all pixels without automation, for example all blur and anti-aliasing is made by placing pixels "manually"