Fuel is measured as it is sold, so presumably this is the primary system for knowing when they will need a refill.
I would guess the delivery driver dips the tank as a failsafe, because spilling fuel is a Big Deal - whether it's an overflow or perhaps even just filling a tank that is leaking.
(I do agree with GP's point about the administration's need to villainize Iran to maintain whatever support they can for the Epstein war though)