The High Court cannot decide on non legal issues
With respect, yes it can, depending on the type of case brought and the governing legislation. I’m not familiar with the FBD case but the High Court has a jurisdiction known as “equitable jurisdiction” which it can (and does), invoke and which looks precisely at non-legal and “fairness” issues.
Further, where a party brings Judicial Review proceedings, the Court is asked, usually, to examine the process surrounding the reaching of a decision by the public body concerned. This often involves looking at distinctly “non-law” issues such as internal processes, decisions reached, reasonableness, proportionality, convening meetings held etc.
It is certainly true that the High Court has appellate and pure legal jurisdiction in some cases e.g, “on a point of law”, where it is limited to the discrete legal point, but to state that the High Court is limited to legal issues exclusively doesn’t paint the full picture.
I know from my own experience that where a public body was reaching decisions and such decisions were squarely the matter of a High Court case, it was incumbent on the public body concerned to proceed with caution pending the outcome of the Court decision. Sometimes this meant that all decision making processes of the public body that were relevant to the Court case were placed on hold pending the determination of the Court.