I don't believe either aircraft commander was to blame here - assuming the 73 was in front of the runway taxi holding position.
The airport authority should have proceduralised - probably through NATS - the types and categories of a/c which could hold at the taxiway holding points, and those which could pass behind. It would appear that this has somehow broken down, resulting in the collision.
Interesting to hear MA's view on it - they're not normally slow at making comment on PPP!
Pleased to hear no-one was injured whatever the reason.
SW