In the second half of the sentence, "I just think they are noisy", put yourself in the situation. You can imagine an alley with old houses on both sides and people's own lives behind every window. One of them, a gentleman with an octagonal beard, squatted at the table and wrote the sentence "I just think they are noisy" with a frown.
The reason why "people's joys and sorrows are not connected" is only because in everyone's life, joys and sorrows occur at different times. A sick person may still be addicted to a game of cards two days ago, and a family may sing a phonograph and someone may die the next day. Everyone's life is an independent chain, linked by one link, and sometimes there are joys and sorrows. This "isolation" is a normal and reasonable state, and there is no need to satirize it as indifference.
Lu Xun is an outsider.
Lu Xun described what was happening as an outsider. Although the description indirectly proves that human emotions are different, it does not mean that Mr. Lu Xun is a person without emotional ability, and Mr. Lu Xun separates himself from the world.
Simply on the issue of emotional connection, "I just think they are noisy" only proves from the side that human sorrows and joys are really unconnected. Mr. Lu Xun used double affirmation to describe the theme he expressed, which is a must.