It's both. It's not like "sideloading" is a part of natural language that just happened to evolve this way to describe the practice. The terminology was consciously chosen by the same people who designed the OS to describe it. The people who argue against using this term aren't doing it in some accusatory way, like "you use this term, therefore you're an evil brainwashed minion of the enemy", but rather by using language to not set up their argument on the enemy's terms, no matter how insignificant.

It's like how "jaywalking/jay walking" was popularized - the term itself was pretty crass for the time, the word "jay" conjuring thoughts of some kind of drooling, unintelligent yokel. Back when car infrastructure was still in its infancy, how would you argue that cars shouldn't dominate all streets and cities when the government- and industry-approved name for your action was literally "stupid walking"?