NOTAMs Notice To Airmen, is really just a notice board advising airmen that facilities at airports have alter status (maintenance etc), temporary changes to arrival departure procedures, airspace restrictions due to weather or other reasons.
Think of them as road traffic reports of holdups, diversions, roadworks etc, but for planes.
The grounding of planes is more likely so they or the passengers/cargo can be checked.
Reported earlier was the news that a small quantity of uranium was detected at London Heathrow. This may be relevant/related.