I believe that you should keep the BB at home for the first 4/5weeks, just to let the BB settle into the world and familiarise themselves with people and so forth. Whether you are chinese or not.
As opposed to letting your BB start to immune from the germs in the environment and so forth... if you have your windows opened, they will still come in contact with the germs and pollution of the air, without close contact with people, and their germs, etc.
The Chinese believe that a BB in its first month should not (maybe bad luck) be allowed to leave its home, and to not go and visit/see people. That is why they usually hold a "1st month old" Baby banquet, inviting all relatives/friends to celebrate the arrival of the BB into the community.
Which is why the chinese man you met, barbwong_130, was sooo surprised.
Though, if you were the only person left in the house looking after the BB at home, and you had to see the Doc's or something, then you will have to take your BB with you. Ideally, best if you can arrange for someone to stay with the BB at home, whilst you're out.