[markem]

Welcome to the real world. You can quit any time you want (barring a contract and some other niggling details in certain industries) and your employer can fire you any time they want (barring protected issues, contract (including union membership), etc., etc.)

The connected world makes it much easier to document behaviors that employers can feel threatened or embarrassed by and thus makes it much easier to dismiss an employee.

For this specific case, it isn't clear if this was a "last straw" or something else.