I think what he means is that he (assuming it’s a “he” here for simplicity) starts with a line in 3D, and along that line he has a number of control points. These control points would be ordered from start to finish. Now, in order to compute a point not lying on the line, but following the general shape of the line, one could use the cross-product between two consecutive control points. Having computed a number of such points off the line, it would be fairly simple to “stitch” them together into triangles, now that there are points both on the line and away from it.
I would recommend trying to draw it on paper before implementing it. Hopefully, if my explanation is clear enough, it will all fall into place.