In addition to the driver living in the area or that a third party could have removed them (via public or private transport), other possibilities include:
that they work nearby
have family or friends who live in walking distance (or have access to other nearby temporary accommodations)
are otherwise familiar with the area from past experience
were picked up a short distance later by CA herself using another, unknown vehicle (this would depend on CA being familiar enough with streetside CCTV/doorbell cams to know or suspect that that stretch of street parking can be viewed on camera and also wanting to avoid those cameras)
Motivations for doing this invariably have to include, however unlikely, that they believed they were doing CA a favor or that she compensated them in some way for doing so. Pathologically helpful, compliant people—allergic to rocking certain rickety, water-logged boats to the extent that they skip work or tell white lies or lies by omission to their partners to keep others afloat—sometimes attract very likeminded, rather credulous folk.
This, I suppose, is the best case but least likely scenario. No real foul play. Just parlor games from people that may lack street smarts. Probably not what happened, but it’s useful to remind ourselves how people pleasers process/collapse under their many burdens in sometimes radically passive, conflict-avoidant fashion.
Any road, I wonder what specific events the police have in mind when alluding to a spectrum that spans “serious crime” to “imminently dangerous medical emergency,” involving a car interior doused in cleaning liquid. I’m guessing this isn’t meant to be taken literally, that they know to some extent she has been victimized, and the “medical emergency” is improbable CYA hedging.