The javascript in the HTML code uses the google maps API. https://developers.google.com/maps/web/ The Electron itself doesn’t know anything about google maps. It only publishes it’s current location to the Particle cloud.
To use the code yourself, you can just copy it onto your own server (or even just run it locally in a browser) and update the google map api key.
My code uses javascript to subscribe to the particle cloud and listen for events coming from the electron. When it sees one, it uses the google maps api to plot it on the webpage. If you modify the javascript to look at the device id, you can display each location event as a separate device. We did something similar for Makerfaire this year with Particle. We had backpacks with the asset tracker in them and showed a map in the booth that showed where everyone with an asset tracker backpack was. The code for that project is here: