Before you say that it should be just a line, let me say that it doesn't break the rules that say you can "draw" a circle with 100 or 12 or 7 dots. The dots don't form a circle but rather fall on the line of a circle your mind draws. Since there is nothing truly between the dots, the "true" shape could jut out and form a corner or any other shape, just like it could be a line between the two dots. The circle isn't really there in any circle of n points, so n=2 (and n=1 for that matter) work just fine.

From Wikipedia:

A circle can be defined as the curve traced out by a point that moves so that its distance from a given point is constant.