That's right. Dave's article is poor in details but let's assume "two thirds of the size of Manhattan" refers to the longest dimension of said island.

According to Wikipedia, "Manhattan Island is 22.7 square miles (59 km2) in area, 13.4 miles (21.6 km) long and 2.3 miles (3.7 km) wide, at its widest".
2/3 of 21.6 km is 14.4 km. A black hole with that diameter would have a mass about 4.85 x 10^30 kg, i.e. about 2.43 Suns.

The black hole, Antarctica and the whole Earth would no longer orbit the Sun. Instead, it would become the larger partner of the binary Antarctica-Sun star system, with disastrous consequences for the entire solar system, disturbing the orbits of all the planets including the Oort cloud and spraying a shower of rogue planets and asteroids around our star neighbourhood.

In a few million ears one of those rogue objects might reach a planet orbiting Sirius and smash into it. Any dinosaurs living on that planet might wonder what is going on. Little would they know that it was all caused by Dave999's misreading of a quasi-scientific web article lacking some crucial details.