I go through training every year, but I have never been trained to a situation with one crew member stuck in the lav. So what? What's your point?
I don't see anything wrong with FOs actions. There was no immediate threat, so why not talk to ATC or to dispatch or to anybody else? They're there to assist you, right?
Nor you want to spiral down to a first grass strip within a gliding distance if you're not sure that there is an imminent threat to the a/c.
As far as Captain's actions, I don't really see anything wrong either. Imagine yourself stuck in the lav, unable to get out. There is friendly pax that tries to help, but you're still stuck there. What you do you do? You want to alert your crew, but they probably won't believe the passenger, right? They're in their fortress, peeking with suspicion through a peep hole. So you give him a password. What's the alternative?
So, before you convince yourself that your thousands of hours set you apart from regular folks (or the "regional guys"), look at the situation. It could happen that one day you will make an a$$ of yourself despite your experience. Has happened before, amigo.