answered in the leaked script.
The predator gets captured by Stargazer, which had done a deal with the "Baddie" Predator faction to "survive" through future baddie Predator incursions.
His "killing spree" is mostly Stargazer staff... which... was fair game.
His goal was to make it to the base where the emissary predators where living.
Movie makes 0 f**king sense.
Complete botch job.