The skill-based / thinking-based are feature indicators calculated automatically by the GameRefinery's model for all analyzed games. The numbers are determined by a number of Core game-related features and the two indicators add up to 100%.

Skill-based - Game's emphasis on speed, aiming and/or steering.
​Thinking-based - Game's emphasis on tactical & strategic thinking and/or logical puzzle solving.

You should think of Skill-based vs. Thinking-based as a spectrum, e.g. how heavily the game's feature set is leaning towards the way or the other when compared to other games.