It's BS speculation. (and false)

It's BS speculation from the tin-hat wing, frequently cut-and-pasted on this site. At Google there is a finite time between when you delete something and when it has to become unreachable through all frontends and APIs, and when it later has to cease to exist, and then finally when the last backup of the data must have been wiped. Source: I personally had to implement the monitoring and alerting that ensures this is the case for a major, privacy-sensitive Google product.

However you should note that if you used a managed Google account, such as educational or corporate account, your ability to truly delete anything may be curtailed by your domain's administration.