Your 18-months son walked into other's driveway. The lady shouldn't scream to you. If you said:" I am sorry" and walked away with your son, you are decent and have higher level than the lady. You should realise it is your responsibility to keep your son out of other's property.
However, you asked the lady why not put a door on the driveway (it is very ridiculous). then you slanged the lady in Chinese ( it is very very rude). Since she is also low level, she slanged back in Chinese.