If the feature sounds familiar, it might be because it is already used on a couple of other services. TikTok uses a similar pulsing ring effect on a channel's profile picture if they're live streaming when you scroll past their video in your feed.
Instagram also shows a colourful ring around the profile pictures of live streaming accounts when they're shown at the top of your feed.
Like Stories, which originally started out as a Snapchat feature before being rapidly cloned by basically every other platform out there, it seems the live ring UI was too perfect to not integrate into YouTube.
But the biggest example of the inspiration YouTube is taking from TikTok is undoubtedly 'Shorts', a feature that lets you browse short-form video content using a vertically scrolling feed.