Fun fact : one method of drug transfer (mentioned in popular media) from Pakistan (bordering Punjab) to Punjab is discus throw [2]. Here, a local athlete takes a disk of drugs and throws it over the border which is then intercepted by dealers in Punjab. A great movie about the drug trade in Punjab is "Udta Punjab" (literally translated as flying-Punjab or high-Punjab).
I can only imagine how many drones they missed. Drones usually fly at an altitude that our eye can't see. The drone operators must be smart enough to fly during cloudy days and during night time making binoculars useless as well. My best guess would be ground intelligence by police.
I am a bit surprised that drug trade in a state in India is using drones. The cost of drones (even commercial ones cost ~$500) is a pretty steep one when converted to Indian currency (~40,000 INR). The article[1] states that the police shot down >100 drones = INR 40,00,000. There must be a lot of money in local drugs in Punjab for the operators to be willing to sacrifice 100+ drones.
[1] https://www.hindustantimes.com/cities/chandigarh-news/107-dr...