I got an email for this and believe it's a targeted deal. Google One members can get three months of YouTube Premium for free (worth $45) which allows you to enjoy YouTube and YouTube Music ad-free, offline, and in the background. Standard trial is only one month. The subscription needs to be activated by 31st October and is only available for those who have activated a Google One account by 30/09/2020. Offer is not available to customers who currently have, or have previously had, a subscription or free trial of YouTube Premium (previously YouTube Red), YouTube Music Premium or Google Play Music.
For those that don't know, Google One is the subscription management service for additional Google cloud storage (i.e. space for Gmail, Google Photos, Google Drive, etc). Why it needed to be its own website and service name, I have no clue ..