As a person working in a field close to data engineering this sounds like they're actually honest about the process.
Tldr: it's not possible to "just delete" everything at once, even though we'd love to be able to.
There's so many layers of where information is stored, and such insane amounts of data in their data platform. so running a clean up job to delete a single persons data in oltp databases, data lakes, dwh's, backups, etc, would both be expensive and inefficient. Instead what they then do is to do it in stages: flip a flag somewhere (is_deleted = true) which lets it be removed from view initially, and then running periodic clean-up jobs.