The visual reference required to go below minima on a NPA under EU ops are as follows;
VISUAL REFERENCE
The pilot shall not continue an approach below minimum
descent height unless at least one of the following
elements is distinctly visible and identifiable to the
pilot:
– elements of the approach light system,
– threshold, threshold markings, threshold lights or
threshold identification lights,
– visual glide slope indicator,
– touchdown zone or touchdown zone markings,
– TDZ,
The requirements in the Lion Air ops manual are similar but I can't cut and paste them. They are in the report if you care to read it. Since the crew had sight of approach lights and runway end indicator lights they would have been fully legal to continue below minima. Having probably justifyably gone below minima the problem they were then faced with was at what stage do you then throw the approach away if the runway does not become visual as expected. The lion Air manual goes on to say that a go-round should be performed if visual reference cannot be maintained but it does not specifly a minmum level of visual reference. It does not specify that the runway must be in sight.
This is not as clear cut as a crew busting minima and anyone who thinks it is really needs to do a bit more study.