It seems a new feature is being rolled out to Indian users by WhatsApp, which allows users to stream a video for watching, without having to download it. And it has a new interface too.
Earlier, you would see the video as ready to play if downloaded, otherwise you would see a download button in the middle of the thumbnail to let you begin the download.
Among the three screenshots in the pic above, the left most image shows how the video looks in the new UI, when you receive it. It gets you two options, download (left bottom now instead of middle) and play (stream, in the middle).
Hitting the Play button opens up the video and starts streaming it, as you can see in the image in the middle. It shows how much has been buffered, while playing the video.
The last image shows the video as download, which is what you get when click on the download button in the bottom left corner in the image 1 above.