Yeah especially if it's late at night with no other options immediately available. I, myself have got into a car with a stranger one time when I got off the bus a stop too late down Midland way. It was late at night and I had no idea where I was going, a stranger pulled up and offered me a lift. Being lost (although the victims from Claremont were not,) and stranded, he didn't seem dodgy at a cursory glance and I was stuck. So I accepted and got into a car with a stranger. I was sober when I did this (it's likely the Clarmonet victims would have been a little bit tipsy so judgement would have been impaired,) so it's not completely unheard of. I ended up getting freaked out and paranoid and got out of the car. This was in the 2000s as well. I was around 18 when this happened.
What I'm getting at, is that it was late at night and they were alone. If a good looking and charming dude offered you a lift, it's not entirely outside the realm of possibility that they would have thought "he seems safe" and jumped in.