That figure is real hard to refute, or square with any other cause of reduction of measles infections except vaccination.
(as an aside, it's really weird that the (first few) comments here on HN seem a little adversarial; I wonder if maybe some people looked at the headline only and assumed it was attempting some sort of anti-vax argument, which the article isn't doing at all.)
So what was reducing the case-fatality rate? I don't know, but it might have been nutrition. There's evidence at least that Vitamin A makes measles less severe/deadly.
Sanitation, antibiotics, oral rehydration therapy, machine ventilation, nutrition, and so on.
It's not the measles itself that was the cause of most fatalities, it was the pneumonia, diahrrea, and other opportunistic infections that come with it.