The landlord wasn’t stealing gas. They piped in gas illegally from the next door building that they also owned, to the tenants, because the gas line to that building was too small. They did this in order to rent newly renovated apartments right away before Con Ed changed the main gas supply to the building.
Your second and third sentence appear to contradict your first.
From the article:
building at 119 Second Avenue, owned by the same landlord