Answer:
He probably meant that the aim of writing The Jungle was not met as the public were fixated at some other thing.
Explanation:
Upton Sinclair is the author of The Jungle where he exposed the harsh working conditions of meat workers and how badly the meats were preserved and processed.
He said that he aimed at the heart of the public and mistakenly hit their stomach which means that his book was meant to evoke pity in the readers for the abuse the meat industry worker faced, but instead they were more concerned with their stomachs which was the contaminated meat they have been eating.
