What counts towards these achievements?

I finished the game last night and didn't get either of these and was a bit surprised.

I'm sure I killed more than 100 just using reckoning.

I also killed a tonne of guys with traps and backstabs, none of it counted, seems like this would be really hard to get with a finesse build.

@Kidavenger: I haven't passed the game but I did get the "They didn't see it coming" achievement today. And I've don't a lot of backstabbing and only a couple of traps. I think you can see your stats in the menu, so I would suggest checking that out.

Reckoning doesn't count, backstabs dont either they are just super melee crits basically.

By abilities they mean killed by the direct dammage abilities. So yes it would be hard to get with finesse build. Mages get it super easy. Pure finesse has to pretty much rely on leveled Shadow Flare at close ranges to get it.