I will pick on that lie to state my point. If you have been to any of the smaller metros in India, you generally get thru immigration at Mumbai before taking a flight from the domestic terminal. Getting to the domestic terminal from the international terminal is cumbersome. You are escorted in a bus operated by the Airport Authority of India, accompanied by security personel.
The aspect of the ride that is of interest is the route taken by the bus. The bus operated within the premises of the airport often running along side the tarmac and taxi way thru numerous and repeated security check-points while it meanders to or from the domestic terminal. This gives you the best view of the runways at ground level in slow speed often around 15 kmph and includes a section of the ride around the cargo terminals.
Most international airlines operate to and out of Mumbai during the night often after 12 AM. I have taken this ride on at least 3 occasions and have not seen a single individual sleeping on the tarmac on even one occasion.
What the author might be referring to could be the people you find in a semi sleep state around the terminal, more so near the cargo terminals. These are employees in the cargo section often on a break. The employees are usually uniformed and any one can observe the security batches hanging around their necks.
You would then have to assume that the intent of the author is intentional mis-representation and sensationalism. Take everything written with a large serving of salt.