That system was developed by the original City of Abandoned Ships. It is explained in the included manual, Age_of_Pirates_2_-_City_of_Abandoned_Ships_-_UK_Manual_-_PC.pdf, page 12.
But looking at the ERAS 2 mod code, it seems to be working differently than in the manual: How much insight or reaction etc the character has affects how fast the skills that are affected by those skills get experience points.
