You hit the nail on the head: your own confidence helped you. You were in a place where no one knew your speech patterns and everyone was a stranger, so you didn't have to worry about it. We know stuttering can happen for any and all reasons, but usually when you're relaxed you have more fluent days. I would then say your own disappointment at coming back home heightened your anxiety, (and we all know what stress and anxiety does to our speech) and now you stutter more because of it. Try a perspective shift: instead of being confident in your speech because no one knows you stutter, try keeping in mind your loved ones know you stutter and accept you for how you are. And strangers don't know you stutter, too! You said you weren't going to take any BS while abroad, you can do this at home too.