According to the original article I cited, continental drift was taken into account:

While geologists theorize that the land that now makes up Antarctica was once a part of other continents closer to the equator-hundreds of millions of years ago-the warmer climate that supported the ostracods would have existed “when Antarctica was pretty much in its current location,” said study co-author David Marchant of Boston University.

I also didn’t excerpt the last sentence of the article:

Marchant said climatologists are uncertain exactly what caused this intense period of cooling.

At least there seems to be a consensus that the scientists have no clue what caused it.