Ptkay:
How many times do you need to be told that if you really don't know what you are talking about, then keep quiet.
The cloud base is irrelevant and plays no part in the minima for a precision approach as far as commencing and making the approach is concerned.
METARS are irrelevant.
The only thing that IS relevant is the ACTUAL RVR passed to the crew at the decision point on this precision approach (except in so much that the DH on a CAT 1 approach could well be the limiting factor).
Under JARs, it is perfectly legal to commence an approach if the touch down RVR is below minima provided that, AT THE DECISION POINT, the RVR is at or above minima. After the Decision Point (which could be defined as at the OM or 4 DME etc) the RVR can fall below the minima again and the approach can be contined to DH. (If no DME is involved in the approach, then this point becomes defined as 1,000 ft AAL).
To summarise, unless you know what RVR was passed to this aircraft AT THE DECISION POINT during this approach then you are talking absolute b*llocks.
If you don't really know what you are talking about then it is better to keep quiet rather than open your mouth and confirm the fact!
I have a pretty good idea about what might have happened, but even with 50years of experience, I would not dream of suggesting this on this forum. How can you possibly state that the crew obviously landed below their minimums?