The package dev.andresdavidcalderon.integral, from now on "the app", does not send data outside of the user's device, as it lacks any online functionality, and does not store any data on the device. The developer, Andres David Calderon, does not have access to any data of the user or device, and there are no ads or any other third party services that may collect data. The system shares data with the app according to the complications you use, but such data is not collected. Understand collected as transmitted off the device.
The app, which is a watchface, is made with watchfacemaker in the XML format, which only includes declarative instructions and resources, but not code written by the developer, at least in the case of the integral formulas watchface.