When SEH was evacuated as a result of the Coronado Hills fire, the Twin Oaks extension was closed. This makes sense since that was the direction the fire was coming from.
Because of the weather conditions associated with wildfires here (i.e. easterly winds), I would expect any future evacuations would also see possible closures of the Twin Oaks extension and the road to Escondido through Elfin Forest. In reality, San Elijo Road to Rancho Santa Fe is the only viable way out.
All that being said, is SEH a fire trap? No, a fire trap is a situation where the only way out is into the approaching fire. Think Wildcat Canyon back during the Cedar fire. That was a fire trap.