The bottom image was missing any sort of preview and the top adds a preview.

This might illustrate it a little better:

Before

After

Sorry I didn’t make it look a bit better…its 2 versions of my same post… The bottom one from some time ago before this update, no preview, just a grey box . … The top one from today after the update, with a nice new preview of the YouTube video

It previously just showed a grey box to the right hand side, whereas now it shows a video thumbnail of the link.