Probably using the YouTube API to embed video, so technically the video source is still directly from YT. It's like what I do for my website, I use their API to automatically update video lists and etc. It's all streamed from YT. Only difference is I just add my own stuff, but in practice I can link anyone's stuff just need the link.
That one probably has a full on script doing the work thus just about anything or anyone is on there.
That one probably has a full on script doing the work thus just about anything or anyone is on there.