He didn't clarify it in the article, but deletes are basically flagged by a "deleted" column, and updates are implemented as delete/insert. The overriding idea

He didn't clarify it in the article, but deletes are basically flagged by a "deleted" column, and updates are implemented as delete/insert. The overriding idea is that a row is never overwritten; storage is write-only. Containers are periodically merged into larger containers (an LSM tree), and deletes are purged at that time.