The pathlist is an array.
The length returns the number of elements (cells) in the pathlist.
Pathlist[0] is the Source, Pathlist[pathlist.length-1] is the destination.
In the case of neighbouring cells, you have 1 the start, 2 the destination. Pathlist's length = 2
Works like the array plugin.
The trickyness comes from the fact that the very first cell (pathlist[0]) is always the source coordinates.
I might indicate/make this clearer in the documentation I guess.
Also atm I'm not working on the behavior. Bug reported have been fixed, it sounds like everything should work as intended.
So if you find bugs or have troubleshooting questions, I'm here to answer, no problem.