It's gotta be the case. Probably choose trip db based on cutting map into squares or hexagons. Dump all location data from drivers and riders into it real time. Sounds like they've got batch jobs running against these databases to discover surge areas and stuff. Probably designed to only hit only 1-2 databases at a time for calculations they do a lot.

This really looks like a crap design overall for a company started well in the age of nosql and stream processing.