A judge in a civil case makes a judgment justifying it by similar decision made in somewhat relevant case.
A party to the case is dissatisfied with the judgment. They find a more recent and, more importantly, much more closely related case (same court) in which the decision was the opposite.
Can what the judge did be called "error of law" for the purposes of appeal?
On an issue of pure law, an appellate court decides if the trial judge got it right or wrong from scratch, and if there is a case that is a better match than the one that the judge used that leads to a different outcome in the case, then an appellate court is likely to find that the trial court's ruling is a reversible error.
On an issue of mixed fact and law, or on a legal issue where a judge has more discretion in how the law is applied (like many evidentiary issues), a judge is given more deference, and the judge will generally only be reversed if no reasonable judge could have applied the correct law to the facts viewed in the light in which the judge saw them, and then, only if an application of the correct law to the facts viewed in the light in which the judge saw them would have changed the outcome of the case. There are a couple of ways that this standard of review is described, one of which is called "abuse of discretion" review.
The judge is required to decide the case on the basis of the law the parties argue. If neither party draws the judge’s attention to a relevant case it would not be an error of law for the judge to not consider it. Indeed, it would likely be an error of law (denial of natural justice or breach of procedural fairness) if the judge did consider it without hearing argument on it.
There may be scope for appeal if the relevant decision was handed down between final argument and the decision.
