Normally LNG is considered as clean fuel.
If released in open area, It is not prone for explosion.
Still, Blast load consideration is requested by clients of LNG on-shore plants.
Is it due to possibility of ethane, propane presence in the Plant.
It is not necessitated in other hydrocarbon onshore plants.

Is there anything I am missing ? someone please clear the doubt.

As a liquid, LNG is not explosive and so it is the vapor cloud released in an open area.
I guess the concerns are related to BLEVE hazards by similitude with LPG. However, some studies concluded that a BLEVE event in unlikely for LNG, mainly because the design of tanks.

In the end I think is about Owner's decision.