almost all packages in any linux distribution are not created by the actual developers of the applications. this is what linux distributions do. they take applications they find useful and package them for their distribution. i have been a maintainer of such packages myself.
this behavior is expected and what you want because you probably don't want to keep up with all the distributions out there and maintain packages of your application for them. most distributions also won't allow you to submit a package unless you are a verified member of their packaging team.
consider those packagers as contributors to your application
Hey, not sure how this usually works with arch but I (the maintainer) didn't create that package but it definitely is based on this somo. Why would someone else register a package by someone else? Only bad reasons come to my mind but I don't know how things are on AUR...