> Nearly every usage of "fella" I've heard has implied that it referred to a male.
Neat, and I've heard it implied multiple times to refer to generic groups of people, in US English as well too just like you. The thing though we need to consider is definitions, facts, sentence context, and even the auhtor's intent much more heavily then both of our personal experiences.
It can easily be argued based on context that the author's intent was to refer to a group of people generically, they even used the "nonstandard" and generic version of the word.
Nearly every usage of "fella" I've heard has had a "male" implication. At least in US English.