It does mention the word "skills" after combo in the text, so it is possible it is meant to encompass multiple types of combo skills. Otherwise it would say "the combo skill" rather than "combo skills".

or is that too pedantic?

Normaly the weapon has flavor text and the pop out is the type of skill it is

such as traumatize, the pop out tells u what it is.

Maybe the pop out for deathcult combo should be Combo: increases attack speed and critical chance for each consecutive hit.

or w/e it does

that being said however, one is called combo, and the other is called deathcult combo, so rules as written i would say no. i too would like some clarification

yeah a crusader is not an Astartes either so i don't see why it would be specific to them.

Fair enough, in simple terms I think it goes without question that it would be the case because the skill trees are not class specific. I'll be playing soon and able to test it if we haven't had a response. 

I believe some melee weapon have "combo" as one of thier effects when mousing over the ability. I'd presume its just these but I can't remember if the death blades state themselves have this specific weapon / ability effect.