You guys need to cut the OP some slack for asking a reasonable question in what is supposed to be the premier M3 forum, especially considering that terms differ worldwide (and the OP is posting from South Africa).
Non synthetic motor oil IS considered to be mineral oil (the process of refining a barrel of oil is to separate it into base - or mineral - oils). And is called that in other parts of the world. Chill a bit.
And OP you are ok if you only added a liter or less of non-synthetic/mineral oil in a pinch.