Unorthodox is maybe a bit strong, but what they're saying is that it's a novel application of an existing technique from another field. Fairly often you will see big breakthroughs like this in maths, where someone has the insight to see that there are parallels between two seemingly unconnected areas of maths, and you can use ideas from one area to give you insight in to the other area.

The tricky bit is that these connections between areas are not usually obvious, so to see the similarity can require a considerable step in understanding.