Home defender could have simply done a callout.
Unfortunately, I think the residents had already missed that exit on this particular highway.
It's 11pm. The man/woman at the door is covering the peephole. The neighborhood (the residents' past history, etc) is apparently sketchy enough that this sets off alarm bells.
The residents called the cops: Great choice imho.
Maybe I'm too old, but if people are knocking at 11pm and not ID'ing themselves, they are probably not on my "friends list."
Whoever is out there WANTS you to answer the door blindly. That's in their tactical advantage. I"m voting for hunkering down and calling for the police, AR or no.