They are not stressed out about the door being left open. They don't understand what it is for. They were probably glad to get outside when they woke up.
If it is raining and they are walking around outside, it is certainly not too cold. Even if it were snowing instead of raining it would not be too cold. At 2 years old, they can easily handle that weather.
The risk of not locking the door is that a predator might find them. I accidentally leave my pop door open a couple of times a year, usually around the change to or from daylight saving time when my routine gets messed up. Nothing has found them yet, but, yes, there is a risk. Predators don't find them each and every time you don't lock them up but the risk is certainly there. I'm not happy with myself when I forget to lock them up.
You don't want their feed to mold. It should not bother the chickens whether the feed is wet or not, but if it gets moldy it can be dangerous for them. Some people routinely wet the feed and their chickens really like it. But if your chickens don't clean it up before too long, I'd change it. I let mine run out of feed about once a week just so they clean up everything in the feeder to keep it fresh. When it gets wet, they get nothing more until they clean it up.
From a predator viewpoint you were lucky but leaving the pop door open is something that is not that unusual for some of us. When I first started reading your post, I was expecting a less happy outcome. Be grateful and stop beating yourself up. It will probably be at least another two years before you forget again.
