The race management statement specifies that a one-liter sample of fuel could not be taken from the Williams race car. Article 6.5.2 of the technical regulations requires F1 cars to finish qualifying and the race with at least one liter of fuel in order to allow measurements on the fuel used during the sessions.
The race stewards considered that it could have given an advantage to the driver and therefore decided to disqualify Albon. Consequently, the Thai driver will start last but will still be allowed to take part in the Australian Grand Prix.