I know very little about which metrics to look at but this seems like an even more wrong metric to go by. What does number of app reviews prove other than that the app is good at pushing people to review it?
Both apps don't urge users to go review their app on the play store. On this assumption, since both serve similar demographic of users - the average number of reviews written per week has to have a strong correlation to number of new users.
I think you're right. Flipkart is very aggressive with pushing their app. At one point they converted their website into just a big link to the play store. I never bought a single item from flipkart after that. I'd rather pay more than do business with a user-hostile company.