Clarification from FFG regarding the definition of "threat area":
Question: Are encounter cards which are attached to one of your player cards (like for example Threads) of Reality) also considered to be in your Threat Area?
Answer: Encounter cards attached to cards in your play area (or locations, or to your investigator itself) are not considered to be in your threat area. Generally speaking, the only cards that are in your threat area are enemies engaged with you and cards that are explicitly added to your threat area by a card effect.