You are correct in Libya having the highest African GDP per capita before 2011 [1]. Granted, Libya's economy is more similar to its oil-producing peers in the Middle East and North Africa.

The debt motive for the invasion makes little sense. American banks made more money on Ghadaffi's Libya [2].

[1] http://data.worldbank.org/indicator/NY.GDP.PCAP.CD?locations...

[2] https://www.nytimes.com/2016/06/14/business/dealbook/libyan-...

As context, that website is said to be a proponent of conspiracy theories (https://en.wikipedia.org/wiki/Michel_Chossudovsky#Centre_for...)