How did the archaeologists prove that people from the Harappan civilization had an idea of 'Privacy'?

The buildings didn't have windows on the lower level, the main entrance didn't give direct admission to the courtyard.

The correct answer is Option 1  - The buildings didn't have windows on the lower level, the main entrance didn't give direct admission to the courtyard.

The Lower Town of Mohenjodaro showcases diverse examples of residential structures.
In the lower town, the common citizenry lived. Several buildings were built on the platform and even the lower town was walled.
The domestic architecture in Mohenjodaro, a city of the Harappan civilization, exhibited several distinct features:
Courtyard-centered design: Many residential buildings in Mohenjodaro were organized around a central courtyard. The courtyard served as a focal point for various domestic activities and provided open space for tasks like cooking, weaving, and social interactions.
Privacy considerations: An interesting aspect of the architecture was the apparent emphasis on privacy.
Ground-level walls typically lacked windows, ensuring privacy within the household. The main entrance of the houses also did not offer a direct view into the interior of the courtyard, further contributing to privacy.
Multi-storey structures: Some houses exhibited evidence of multiple floors or access to rooftops. Remnants of staircases suggest that vertical expansion was employed in Mohenjo-Daro’s residential architecture.
Wells within houses: Wells were a common feature in Mohenjo-Daro’s houses. Many houses had wells, often located in a room accessible from the outside. These wells provided access to water, not only for the residents but potentially for passers-by as well.