This excerpt from your article did indeed get my attention...
"...About a third of the time, the couple had argued right before the homicide took place, and about 12 percent of the deaths were associated with jealousy. The majority of the victims were under the age of 40....."
I should also like to point out that "romantic partner" doesn't necessarily mean a spouse.
Amateur opinion and speculation
correct, that 55% "intimate partner related" means anyone you're currently or have been in a relationship with or dated AND their families/friends - not just spouses. It's a very broad range. In fact it almost makes the "it's always the husband" trope look quite false.
(and yep, that 'recent argument' thing definitely was interesting.)