TBH I'm not sure what an " ILR landing " is, but anyway:
The original plane for this flight was changed out due to fog at GLA - as far as I know that's normally an A320, which I understand are perfectly capable of an ILR landing in fog.
Not always - If the aircraft was swapped out " for fog" then one strong possibility is the original airframe may have had a temporary minor defect which downgraded it's autoland/all weather operations capability. It happens on all types from time to time to time.
As for PEDs - due to risk of interference with the aircraft systems that you really do need to be working without any risk of compromise on an autoland it's a requirement at BA and other operators that they are turned off for low vis approaches - hence the announcement.
At the end of it all it sounds like you got to your destination safely...........