Hence trust no
Presume you meant "hence trust no one"?
True. Condition yellow and good advice.
But given the typical suburbia mindset (way evident in Collin County!), it just does not cross the average person's mind that a familiar face, an ex-colleague (assuming she even recognized him right off) is a threat. it's not like she was staring down 3 menacing-looking hoodie-wearing thugs. This was someone she knew - maybe did or did not recognize immediately (Huh? he looks famil..oh it's <bang bang>". Condition white. Now Code Blue.