...or rather, why did not the concerned cabin crew notice at the time.
One wonders
Who knows what had happened during the boarding of the aircraft? Perhaps the cabin crew had an unusually high workload and by the time they were standing in their relevant positions, they were windiing down, or perhaps concentrating on other safety related issues so missed the announcement for the location of exits.
the aircraft should have been grounded
Why?
There was actually TOO MUCH information given! The information given would have covered all of the relevant vital things, just with the addition of an upper deck and extra set of doors. They're both Twin Aisle, neither has overwing exits. The demo video points out there are two exits at the rear and two at the front of each cabin section, exactly the same as the B777, theres just more cabin sections on a B747. The safety cards were correct and the video asks you to study them.
Had it been a B747 but the B777 video was shown, then yes, there is a problem as some vital information would have been omitted. This would have required reverting to a manual demonstration conducted by the cabin crew, prior to take off.
Because the information given didn't miss anything out, there is no CAA requirement to ground or delay the aircraft.
Six