Also, I have noticed the BOM have a regular habit of issuing a TAF for good weather, and then amending it when the weather turns bad (or just prior). This might be measured in the KPIs as an accurate forecast, but is not much help for planning a flight. That also appears to have happened in this case.
I regularly ring the BOM if a forecast looks suspect, like fog lingering or METAR disagreeing with the TAF. What I've found is that whatever flags the issues just does not get picked up at country ports, this is even more a problem when they are focused on bad weather at a major port. This is nothing particularly new though, there's a few ports I've flown to that have local conditions that catch the BOM out regularly and are predictable if you have local knowledge.
The weather forecast is an educated guess by professionals trying their best. Always study not only the minimum legal forecasts but surrounding area forecasts and actual condition for prevailing trends, the overall trend picture will be more valuable to planning than hoping on one TAF, it will also show up if the TAF possibly has errors. In this case the weather forecast was not at fault, it was accurate at the time of planning. Possibly there were comprehension issues, GAF issues or not. This was a training flight, the instructor MUST be able to read and understand a GAF, what on earth is being taught to the student if the Instructor has no idea.
The student didn't inform the instructor of the weather from 1400-1500 as they were meant to land and depart before its onset, maybe the instructor had dismissed it in the same way by not reading further on the TAF. The flight ran late an hour or more and because of this omission they ran into the weather. A major part of cross country navigation training should focus on the planning especially in regard to weather. It sounds like this was given a cursory glance and it caught them out.