It does, instead, mandate that the employee is given a 30 (edit: California is 60, federal is 30) day notice that they will be laid off. It would be completely within the law to say "you will be laid off on Feb 4" and require you to work until Feb 4, and not have any sort of additional severance pay.
This seems like a long-winded couching of the simple premise that would explain what happened. The tweet/author is misrepresenting the situation or was promised something he isn't legally entitled to, regardless.
> mandate that the employee is given a 30 day notice that they will be laid off
ie maybe he was terminated with notice and it wasn't explicitly labeled a severance letter.