Can I really tell where the tower is that I'm connected to?
From app blogs Methodology explains how they collect data


Crowd Sourcing (already pointed in comments)
Monitoring users who installed app continuously  


So, the accuracy pretty much depends on how many people use the app with GPS on


Data Analytics


Also see Cell towers/wifi routers not located correctly which is dated but relevant

This app was recently launched in India and I noticed this


Cell towers are very well mapped of a  provider, though, in my area tower density is low ( likely because provider made it open source as a part of publicity )
Cell towers are not well mapped, for another provider,  though the tower density is much higher


Not a very dependable app , IMO