No, Trump-a-L, it is not. There are over 1.1 BILLION iOS devices in the wild and this battery issue is affecting a small subset of the iPhone 6s model and it has been identified to a specific run of batteries, that comprise less than 1% of that 1.1 billion. If it were an OS issue, the number affected would be huge. It's not. Ergo, it isn't an iOS problem nor is it an app issue because none of the battery problem iPhones have the same app on all of them that is also not on all of the rest.
It is not battery related.