Magazines have been called clips for over twenty years in Shadowrun books. Gear tables going back to the core SR1 book, and reloading rules back just as far, have used clip, magazine, and cylinder. It's wrong in real life, but it's right in game, as far as I'm concerned.
Maybe arguments just like this one (and the one that happened last week) happened in-universe around the same time, until eventually everyone arguing for magazine instead of clip in corp-produced gun-rags just threw up their arms and quit, after getting too many threads locked. In fact, that's what actually caused the Crash of '29. Server overloads, too many moderators on too many Matrix message boards, all cried out in terror and then were suddenly silenced.
Echo Mirage did its thing, and when the dust settled and the world kept turning, clip had beaten magazine, officially. Programs were loosed that "corrected" every electronic publication, ever, early AIs and agents were sent off into the darkest corners of the Matrix to take care of this global editing, corporate black ops teams in stealth-painted choppers descended to silence the last few holdouts face to face, and within a matter of years the genocide was complete.
The term "magazine" was quietly shuffled off to refer to internal magazines only, the victorious word "clip" (initially trademarked, and with tremendous profits made due to it winning the Great Term Wars of '29) emerged triumphant, and that's that.
So "clip" is right in-universe, and all the Shadowrun writers for the last twenty years have been doing us a favor, helping with immersion, by purposefully using the "wrong" term in order to help us all stay in character.