A "software update" could very well be the chosen wording for something of a similar nature but less comprehensible by the average traveller.
Was it still foggy in Stansted? If so it is possible that the aicraft was not released for autoland following some previous maintenance action. That normally requires a practice autoland in good weather conditions before being released.
Or as the aircraft had diverted, its 48 hour validity of the ramp inspection could have expired and an engineer had to be shipped from Stansted.
Some MEL's can be signed of by the captain, but some requires the engineer to take some specific actions before release.
Software update... yes maybe, but you all assume it's the nav data base. It could have been related to any computer or control unit in the aircraft.
Remember there's different sort of lies. Many of them are not to harm people but to not worry them or to create misunderstandings. It 's to simplify the message for things that can't that be told without a detailed explanation on how an aircraft works.