I mention this because "Old Pap" had an almost identical failure of nerve eighteen months before the Little Rock fiasco. In February 1862 he abruptly bailed out of Springfield in advance of Curtis's approach from Rolla. Price had no particular tactical reason for skedaddling, he simply panicked as the Federals steadily drew closer and closer. Curtis fully expected Price to put up a stiff fight to defend his Missouri "capital" and was astonished when he bugged out.
Could the same thing have happened in Little Rock? I offer this only as a half-baked suggestion.