It depends on how you've configured the router. It's quite common to reject or drop ingress traffic received on an egress interface destined to a NATed network address. In fact, I would flag any configuration that didn't have that.

Yes, but we've just successfully rewritten the article in the comment section as "it's not having NAT that provides the security itself, but other configuration any sane person would expect on a device doing NAT to prevent unexpected inbound connections" is exactly what the article set out to separate.

Yes, of course. If NAT denied connections in the way people think it does, then it wouldn't be necessary to separately configure the router to reject inbound connections. It's possible to have configurations that don't do that precisely because NAT doesn't do that itself.