One fuel spill does not torpedo the Captain's career. That's a screw up by someone actually handling the valves etc. You read them and their section leader the riot act, given them s**t duty for a month, pull their quals on a few things and have them (re)take training.
There must be more to the story - a history of significant mistakes (ie. the kind that get noticed by command) that indicate leadership failure from the top down.
A 4000 gallon spill while tied up pierside is likely to get you relieved from command, regardless as to who turned what valves.
Doing it while pierside at the Yorktown Weapons Station while loading weapons seals the deal.