I won't argue over preferred nomenclature. I will suggest before you correct the end-user, fix the supplier...
If Marlin made it, and call it a clip, it's a clip(as you can see they have recently started calling it a clip magazine). Same holds true for many manufacturers. The "C" in a Remington 10C is for clip, as with Parkerhale 1200C (where "C" is for clip). If Wikipedia made it, they could call it whatever they want.
It's not like we don't know what OP meant with the term. Calling an ejector an extractor is plain wrong, and will lead to frowns when parts are ordered. Calling a magazine "clip" when it's manufacturer does is anything but wrong. Funny thing language...I called all snowmobiles "ski-doos" for years(regardless of manufacturer), and I know folks that call all tissues "Kleenex".