"Maybe I'm missing something obvious but if the escape velocity has increased 1,000 fold along with the gravity, how exactly has the radius shrunk?"
Because escape velocity is calculated using both the mass and the radius of the earth, specifically it's sqrt(2GM/r). So to achieve the thousand fold increase, you can either keep the mass or radius constant and change the other by a factor of 1,000,000 (Mass up by this value, or radius down by this value), which if you read the rest of the article, they do both these options.
Or you can play and get a variety of options. You could put mass up by 1,000 and radius down by 1,000 and achieve the same result. Or any other factors of 1,000,000 (m up by 2, radius down by 500,000