I'm inclined to doubt the accuracy of the claim, given how saturated left-wing sites are right now with anti-electoral college articles. However, I only know about how the electoral college functions, not what it was created for. Is the Vox article true, half true, pants on fire, or something in between?
So I just answered a similar question here and also I went into some more detail on my blog.
That said, I have never really seen a claim by a legitimate historian stating that the main reason for the electoral college was to protect the south (but this doesn't make the claim necessarily untrue).
Strangely, they assert that had they not adopted this system "the south would have lost every time," only fits if the majority of the population was slave, rather than free, which isn't the case. Rather it benefited the North to have the system, especially at the time of its creation because they had many small states with tiny populations (VT, NH, RI, NJ) that would head much smaller voices had it been a popular vote. Also, if you look at early elections, like the election of 1800, two northern states voted for Jefferson and would have likely done the same if it was a popular vote. This means that northern states would have still had many of their people voting for southern candidates especially since the country was not divided as the nation would be come in the ensuing decades. Granted, some states with high slave populations did benefit more from the system since they could claim more citizens for electoral votes, but by 1800, States like VA still had a white male population that was significantly larger than any other state. Also worth mentioning that one of the biggest proponents of the electoral college system was Alexander Hamilton, who was from New York.