You are connected to a network extender. Cell service providers provide network extenders for use typically within some buildings to boost indoor signal strength. It is especially useful in places where walls block cell signal to people within the building.
These extenders ride on the landline internet service in use by the building. It can also be used to extend the cell service to faraway and remote areas. The extender is a smaller device and cannot cover anywhere near the same area as full blown cell towers.