This shows that the full game installer was too large for a single file and was split into multiple compressed parts. You would need all parts (Part 1, Part 2, etc.) in the same folder to successfully extract the data.
Downloading files from unofficial sources like this carries a high risk of malware or ransomware . If you're looking to play the expansion safely, it is available on official storefronts like Steam, Xbox, and PlayStation. Aliens_Fireteam_Elite_Pathogen-FLT.part2.rar
This stands for FairLight , one of the oldest "Scene" groups known for releasing cracked games. This shows that the full game installer was