That HK mag is just an ambi-mag, that's all
re: clip. I have a rifle designed for them. Two really, but one has a scope now and the clip won't work- an M1 rifle and an M1903A3 rifle. One takes an en bloc and the other a stripper
In WWII, many GIs called magazines 'clips'. You and I know that a clip isn't a mag. Don't let it bug you