Ok, that's some historical revisionism I've not see before. The term sideloading was invented by an internet storage service company to refer to copying files between remote storage buckets without having to do an upload or download. The term then got adopted by the community for copying MP3 files to a player from your computer.
In the communities I participated in, that was just called copying, and generic MP3/MP4 player owners were often quick to point out that they could just simply plug in and copy files like a USB drive, whereas iPods needed iTunes and "syncing". I've never seen sideloading being used to describe anything other than to suggest "impropriety" or something that's not "officially unapproved", and only in the context of applications --- I haven't ever heard of someone "sideloading" music to a player either. I bet for the vast majority of others, this is also the case.
Keep in mind that you're making a somewhat pedantic point about the difference between "invented" and "adopted" and the core of the criticism is still true.
The thing you did with software direct from the developer used to be called "installing" but now the platform companies call it "sideloading" which sounds like something that would cause an airline to lose your luggage.
Maybe in your social surroundings. In some/many other countries - granted, mostly non-English-speaking they just call it (literal translation) "Installing applications from a file" or "Installing APKs".
Whatever, I just think it's useful when evaluating an opinion to know whether the person is prone to fantasising and making shit up. There's way too much of that going around these days.
