probably a mix of both.

From perplexity because i'm lazy:

The core difference is that eMule uses a persistent, pairwise “credit” score that carries over across files and sessions, while BitTorrent uses a short‑term, per‑swarm “tit‑for‑tat” mechanism with no lasting credit between peers

EDIT: Also emule has a block size of 9Mib while bt has a 512kb which at the time (let's say 2005) was too ambitious for the speeds the users had at home. The 9MiB block is now ok :-)