I provided facts as well, so let's use your own sources shall we?
A person in the same position, involved in the same activity, or otherwise associated with another. [1]
You conveniently ignored that when you attempted to mispaint actual facts in your comment. Here I'll even add another source: used of people or a person with whom you share something, esp. the same kind of job, interest, or experience [2]
[1] https://en.oxforddictionaries.com/definition/fellow[2] https://dictionary.cambridge.org/us/dictionary/english/fello...
You linked to "fellow", not "fella".
https://dictionary.cambridge.org/us/dictionary/english/fella
That's precisely why I provided links to two dictionaries. Not the definition google spoon feeds you when you type in "define fella"