Actually (effectively) incredibly secure then...
"...the video stream was only available to those who had a direct link to the video, and was not searchable via YouTube or accessible without the URL."
Unless somebody involved shared the link in a public forum, then it's actually extremely secure. At least effectively so.
Tom Scott has a video about "Will YouTube run out of addresses" (+/-?), where he explains the YouTube URL addressing scheme and its relative 'address space'. He touches on the utter sparsity of it.
So, why don't you try to find Tom Scott's video by randomly trying various YouTube URL strings until you stumble across it?
Actually, try to find ANY YouTube video by random YouTube URL string. See if you can randomly get a hit.