Sorry if this was answered somewhere else and I missed. But, I am correct in understanding that mortal strikes are not multiplied by the threat of a unit or its brutal bonus? I read the rules and it sounded like only "wound" results (the little explosion symbol) gets multiplied by threat. Meaning that damage dealt by other sources, such as mortal strikes (the skull symbol) or surge abilities (like the lancers attacking something with a blight token) don't get to multiply this damage by threat.

Is this correct? Thanks.

Correct.

When you spend a damage result, you deal damage equal to your threat. The other symbols don't interact with threat.

What @Tvayumat said, also damage and wounds are not the same thing. Damage is what's dealt, wounds are what's taken.

Thank you for the clarification!