The Gini coefficient is a relative measure. It is possible for the Gini coefficient of a developing country to rise (due to increasing inequality of income) while the number of people in absolute poverty decreases. This is because the Gini coefficient measures relative, not absolute, wealth.
In Capital in the 21st Century, Piketty is looking at wealth groups (top 1%, top 10%, rest of the population). And it paints a very different picture.
Agreed. Admittedly upon reviewing the article, PG did use it as an effect, not an objective. But at the end of the day he's reasoning from rarified datasets like % of billionaires inheriting their wealth, vs using more broadly meaningful indicators like inequality in healthcare and education access, housing uncertainty, and others. That's what makes him so out of touch.
