Jury nullification?
It's possible that the jury (a single jurist?) thought Blake was justified in some sense.
I think you're right. From the little I've followed it, it seemed that the strategy of the prosecution was to paint the victim as such a despicable piece of trash that anybody stuck with her would have done the same thing, therefore he must be guilty. The defense agreed with the trash assessment. The jurors may have consciously or subconsciously decided that the skank deserved it, and a public service had been performed by the killer. From everything we hear about her, it’s hard to disagree.
Blake took one for the team of humanity, and humanity looked the other way in appreciation. Sets a real bad legal precedent, but sends the right message to trailer trash everywhere.