Type-kun said:
Just wondering if somebody has any idea why the hell does twitter convert uploaded .gif images to .mp4 videos with "gif" mark on the container?
I don't know the "official" reasons, but there are many advantages of a real video over gif. In Twitter's case, they probably like the smaller filesize and the ability to easily pause in the browser. There are other advantages, such as better colors, but that doesn't apply if you're converting from a gif in the first place.
Honestly, gif is almost entirely obsolete and a lot of people use it when there's no reason to, so I can kind of see why Twitter doesn't support them natively (though it is a little nasty to pretend to support them and then do a lossy transcode). I think the only valid use case for gif at this point is when you need animation and transparency, but not alpha transparency, i.e. animated pixel art. Your example happens to be just that, but most gifs aren't; a lot of people try to use gif as a video format, and it's really annoying.
And more importantly, is there any way to get original gifs back?
Looks like no. According to this, it seems the transcode happens on upload and they don't store the original gif. I tried an API request for the tweet you mentioned, and even though its type is "animated_gif", the only variant listed is the mp4. So even if by some chance they do store the original gif somewhere, I don't think there's any way we can get it.