FTA: Our localization approach combines open-source databases (OpenCellID [47], Mozilla Location Services [66], and CellMapper [12]) for PCI-to-coordinate mapping of cell towers with a trilateration technique based on relative signal strengths.
Have you considered that google might just perform poorly compared to other methods?
CellMapper, at least, is not even a little bit open source. It doesn't even have an API.
This leads me to wonder what other details that FA provides which might have been fabricated from thin air.