They tested the plane material at that spot for explosion residue. Which part is confusing?

It isn’t.

CNN just did a story and are saying first reports confirm tests of the damage came back positive for explosive residue.

MSN 642 is operated by Greece’s Hermes Airlines under a wet-lease agreement actually.

There’s a video of the plane landing, from the inside, if anyone wants a look. That also answers maybe why not many victims. Not enough passengers.