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Yes, exRots is the big change between v1 and v2. I wouldn't recommend that people touch this value unless they want to do weird things with the twist of the structure (e.g. for creating screw threads).

The problem is that the standard "rotate an arrow to line up with another arrow" algorithm doesn't consider the initial Z rotation to be important, whereas it's very important for extruding along a path. By default it tries to be intelligent about setting these up to avoid large twists in the structure.

The code might currently be over-compensating, but as a consolation, this exRots is exposed to the outside world to allow for advanced uses where people to define their own pre-rotations.

The demonstration object in the path_extrude.scad code has a kink in it so that it's more obvious what the various parameters are doing, and includes an animation that demonstrates the weirdness that happens from modifying just the first value of exRots.