Packaging is the fact of creating a package. :) Normally this imply a limited amont of work. But there is a team "upstram" that continue to work on it and where bug can be reported (or I can be a "bridge")
Porting mean a lot of work (at least in my head). What does Pickle is usually porting, things like : - translating GL to GLES - hard work on resolution (change textures + a lot of code) - optimizing for arm - etc Usually those who have ported will also fix the bugs (as they are largely involved in the code). Chance that the "upstream" code to be merged later is small (That's why we have mame4all and mame106. The later is a port from a newer release). So in some way it's a fork. (Tuxrace is a clear fork of extreme tuxracer)
I hope that clarify all.