This looks like a couple old enough to be empty nesters so only the two of them in the house.
Besides, they called out to the intruder and yelled that they had a gun. I figure they wouldn't have shot if she had responded to them.
I know if I'm scared, warned the intruder and the only answer I got was the continued approaching footsteps, I'd shoot.
If the intruder had been a 6'3" muscular, male, habitual criminal, we'd be saying how stupid the homeowners were for playing 20 questions before protecting themselves.
That said it's still one of the first rules of firearms handling to positively identify your target before firing. Ironically if a cop had shot someone in similar circumstances he would most likely be working a desk and internal affairs would be giving him an anal probe over the whole thing.
There was stupidity to go around here. How does a 21 yr old recent grad mistake a very unique $2.75 million home for whatever cracker box she most likely lives in? Why would a pair of empty nesters in an urban area like Boulder leave their doors unlocked? Boulder is about a 40 minute drive from the furthest reaches of the Denver metro area and Boulder itself long ago ceased to be bucolic little university town.