I’d bet (a small amount of) money they have no ability to delete accounts at all, and it goes all the way down to foreign key constraints introduced by a well-meaning but inexperienced developer that unnecessarily couple the accounts table to many other records.
Why not just anonymize the data instead? Not using foreign key constraint just for the sake of GDPR sounds weird.
That isn't what he said.
He said their inability to delete an account is due to poor design of their data schema by a well intentioned developer.