From the Github page:

> For this hackathon we used data about whether a street is lit or not from Open Street Map. Later we could incorporate official UK gov data about street lighting or even incorporate satellite imaging data.

It sounds like getting the data right wasn't the focus yet:

> Later we could incorporate many other kinds of data such as safe checkpoints trivially. The core technical challenge was wrangling the data and writing our own custom routing algorithm.

This is a common pattern for OSM. The tool to use the data helps locate areas where the data isn't complete (say you plan a route through an area you know and it doesn't make sense).

Correct the primary data source was open street map.

I'm curious what you're looking for in OSM. I looked at highway=street_lamp and the results were....let's say "sparse".

The lit-key is used on ways and indicates the lighting of it:

https://wiki.openstreetmap.org/wiki/Key:lit

The highway=street_lamp tag indicates that there is a lamppost (which can be a navigational aid), but is a much more detailed form of mapping that should be used in addition to the lit-key on the ways themselves.