I totally see where you're coming from, you just don't get how the term was and often is used. If he had called her a fox, you wouldn't get bent out of shape about her not belonging to the vulpes genus. Unlike fox, MILF is used both literally and figuratively and context generally makes that painfully obvious. Maybe that's news to you, maybe you just refuse to recognize how the slang is being applied. Either way, it was fairly obvious to most that /u/usmauriga wasn't using it literally given the complete lack of anything suggesting she has kids. As I said before:
they only playfully pointing out that a comparison between the exceptionally attractive journalist's perky breasts and the other women's sagging breasts was like comparing apples and oranges.
That last part was kind of integral to the sentence. It wasn't about motherhood. That's just not how MILF was used. You can insist it was and that there is no misunderstanding, you'd just be wrong is all. It was about the comparison of body types that are very different representations of their groups. Nothing more, nothing less.
When was pointed out that it wouldn't be correct if it had been used literally(whether because /u/thisoldhousecat shared your misunderstanding or if it was just a funny observation isn't clear) the following "porn MILF" comment just reiterated that the word could be applied in a figurative manner.
MILF is often used to describe attractive women of a fairly broad age range regardless of whether they actually have kids. This is especially true in porn where they are likely to call someone a MILF because of her age. Certainly, there's no shortage of porn that specifically focuses on the idea that the woman being featured has kids or is pretending to have kids, but that is a specific genre. The term is used more figuratively outside of it. Heck, just looking at urban dictionary it doesn't take long to find definitions that specifically point this out:
MILF A sexually attractive women over the age of 30
MILF acronym for M.other I.'d L.ike to F.uck.
In other words, a hot woman with kids. But a misconception with Milfs is that they don't necessarily have to be mothers. The Milf is also a fetish of good looking older/middle aged women generally in their mid 30's to mid 40's, but don't necessarily have to be mothers. The reason for the fetish is that they are very sexually experienced, but at the same time, not old and dried up, still some pussy juice left in the tank if you will. Jew Guy: Sara Palin is a milf!
Jew Guy 2: True nuff, she has 2 kids right?
Jew Guy: I don't know, I know she has at least one, but even if she didn't have any, she'd still be qualified as a milf.
Jew Guy 2: Hey dumb a**, MILF stands for MOTHER I'd like to FUCK!! Not Woman I'd like to fuck, you dirty kike.
Jew Guy: Listen here you dreidle spinning menorah lighting yeast eating jewish SOB, let me educate you. a hot mother would be considered a milf of course, but milfs don't have to be mothers to be milfs. They have to be in the general age range of a housewife, mid 30's to mid 40's, sometimes into the early 50's if the bitch has enough botox.
Jew Guy 2: You're still a jew...
M.I.L.F. Any woman in her early 30s to late 40s. These women are in danger of being attacked by horny teenaged boys.
The word is used to describe a woman that's too young for some descriptions and too old for others. I'm not even saying I like the term, it's just one that's become fairly commonly used in recent decades and over time had it's use applied to a broader group than its literal meaning covers. By all means, let's popularize something else that can be applied consistently regardless of context, but in the meantime just look at context clues to see how the currently popular slang is being applied.