Odell is talking about the lack of cryptographic ownership and thus, verifiability.

You can't prove a tweet was sent by whoever you think sent it.

On centralized platforms, the companies in charge tend to have either bespoke backdoors, or are downright able to modify and insert tweets via queries against their SQL database (as an example).

In contrast, nostr works with keypairs, where at first stance, only the owner holds the private key, hence only they are able to post on their profile.