As we don't know where in the cycle of the check these photos were taken, you cannot surmise it is not a D check by what is and is not in the photos.
I can surmise it is because BA's 747-400 have been going through Cardiff for D checks and most C checks are still carried out at LHR.
Checks are carried out based on both cycles and age. If an aircraft is in regular use, cycles will be the dominant factor.
If an aircraft spends a long time sitting on the ground between ownerships and is not stored in dry conditions then age will be taken into account.
Again, if an aircraft has been the subject of many leases and has been used by different airlines, serviced by different agencies and generally used very hard, the C and D check cycle might be accelerated for that period of its life.