I was curious about this too and thought it must be a massive GIF. However it's not actually a GIF, it's an MP4 video[1], I wonder why it's mislabelled as a GIF.
[1]: https://video.twimg.com/tweet_video/FV3mdpEXoAIrkA1.mp4
[1]: https://video.twimg.com/tweet_video/FV3mdpEXoAIrkA1.mp4
In the cultural consciousness, a "GIF" represents a particular medium and form factor, which has become decoupled from its namesake file format to deliver the same experience more efficiently.
Then while we’re at it, settle the pronunciation debate by picking a different one for each.