Kong said he only waved his knife in a horizontal fashion several feet away from Miu. His lawyer implied that another member of Kong's gang actually made the cuts.
At trial, Kong's main defence was that someone else stabbed Miu. But "in the alternative", if Kong did stab Miu his lawyer said it was in self-defence. The trial judge didn't think much of the self-defence argument, and wouldn't let it go to the jury. The jury decided that Kong was the stabber and convicted him of manslaughter.
The legal issue now before the Supreme Court of Canada was whether the self-defence theory had an "air of reality", such that the trial judge should have let the jury consider it as a possible reason for acquittal. Obviously, a jury system requires that there be some leeway for juries to hear unlikely factual arguments before a conviction can be allowed.
The majority of the Alberta Court of Appeal didn't think Kong's alternative defence passed the laugh test. The fatal cut was a punching blow while stepping forward into Miu. Kong claimed his only knife move was a slash in the air feet away from the victim. Justice Wittman dissented at the appellate level, but never explains how a defensive slashing of the air while moving back could possibly be consistent with the evidence of the autopsy.
The Supreme Court of Canada unanimously preferred Justice Wittman's dissent, but doesn't say why. They ordered a new trial.
The practice of allowing appeals without providing reasons is a rare one. It may have occurred here because the appeal is as of right. It is obviously important for trial judge's to be very careful about taking any defence away from an accused: the jury system is imperfect, but it's the system we have got. At the same time, there has to be a minimal amount of consistency in a self-defence plea. It is unfortunate (and a measure of bad form) that the SCC didn't at least comment on why they were willing to overrule the lower courts.
Case Comment of R. v. Kong, 2006 SCC 40
Update: Alex's post on this case is here.