I'm working in my first job now for about seven months. Recently our office received some renovation work. Along this we got a new door to our neighbor office which will be always open now to lower the distances between the members of our department. Since than I could hear most conversations they have there. It's nothing secret or anything, but sometimes quite private or off-topic. (There is another office room in the middle, so exactly, there are two open doors between us.)
Recently I heard them talking about one getting a baby soon and I wanted to congratulate them. But as I am shy and hardly ever start communication with them, and when I do it's about work, I found it very creepy to respond to a conversation I was not a part of. The conversation passed and I remain silent.
What would be appropriate/professional in such situations? Should I never respond to anything - or only if it's about work and I could help - or am I overthinking this? Would it be considered as rude if I remain silent? Or should I have a talk with them and come back to the topic later?
I am not bothered to hear them, just not sure how to react.