The wave isn't primarily due to loosening of restrictions or slack in behaviour. It's due to, for a lack of a better term, environmental factors.

Look at the countries in the vicinity of India; they all show similar rise at around the same time.

https://www.worldometers.info/coronavirus/country/pakistan/#...

https://www.worldometers.info/coronavirus/country/bangladesh...

https://www.worldometers.info/coronavirus/country/sri-lanka/...

https://www.worldometers.info/coronavirus/country/maldives/#...

https://www.worldometers.info/coronavirus/country/iran/#grap...

https://www.worldometers.info/coronavirus/country/kazakhstan...

https://www.worldometers.info/coronavirus/country/azerbaijan...

https://www.worldometers.info/coronavirus/country/uzbekistan... ...

COVID is seasonal: https://www.medrxiv.org/content/10.1101/2021.02.28.21252625v...

Mumbai had the peak of its 'first wave' on October 7th. See mobility trends for vehicular and pedestrian traffic at https://covid19.apple.com/mobility. You'll see both monotonically increasing as the peak approaches and then recedes. If this were a simple morality tale of the level of social contact, this wouldn't be the case.

See this paper for a more thorough look at the epidemiological mysteries of an infectious respiratory disease: https://virologyj.biomedcentral.com/articles/10.1186/1743-42...