@Crystal I wish someone with access to a car can help chime in, because apparently neither of us does. It seems silly that we can't agree on how something as ubiquitous as a car door works. It's too bad the author didn't bother explaining. Maybe because all cars in Japan work the same way due to the law or something, or perhaps the author assumes all car behaves the same way.
I tried search ("Googling") about this but it's so difficult, the most common hit was about how to unlock a car if you're accidentally locked out. Which if anything proves that it's a normal, common occurrence. How you can accidentally lock yourself out, though, is also not easy to find. One possibility is of course you simply lose the key, but I'm pretty sure the most common case is leaving the key in the ignition.
Admittedly, I was wrong in one regard. Apparently it's possible to use the key (not the remote) by inserting and turning it. But it's of course just another way of doing it and not at all the only way. And the reason I don't know is because I never had to do that. I've locked a car many times without using the key nor the remote. Although now that I think about it, in one case simply closing the door would cause the lock to spring open again. But there is still a workaround, pull the handle while closing the door. This seems to be modern-ish (last 10-20 years) invention to idiot-proof the car so you can't accidentally lock yourself out.
Still, I'm not aware of any car having a metal protrusion on the door that prevent it from closing. It's common in houses, especially front doors, but car doors behave more like bathroom doors.
Sorry this post is so long. Honestly, I intended to keep this brief as I just want to just end this fruitless conversation, after all as any detective would know, we need some evidence.
The funny thing is that, in some stories we have the hero at the end showing the culprit that "Hey, you can do this you know, bey you didn't know that!" "Whaaaaat!!"
Wish I can do that....