DGMarie-
I think the poster was trying to show the point that Kappa Alpha Theta was officially started as a Greek-letter Fraternity for women, with the ideals of spreading across the nation, a goal which they have realized. To our knowledge, Phi Nu is only at the one college, which means they can't be categorized the same. (international vs. local)
Also, by showing us the examples of Alpha Delta Pi, Phi Mu and Pi Beta Phi, the author of the article is saying "yes, there were secret societies for women before Kappa Alpha Theta, but they did not take on their Greek-letter designations until much later."
Therefore Kappa Alpha Theta still has the right to "The first Greek-letter fraternity, founded for women, that is international in scale."
(BTW, Kappa was founded in 1870, also, we were just a few months after Thetas!)