Their accompanying website [0] says mobile phone data comes from teralytix while car movement data is sourced through inrix [1], which appears to gather data through navigation apps of some sort (vague as can be expected but the linked paper [2] claims that).

[0] https://mcc-berlin-ariadne.shinyapps.io/dticket-tracker/

[1] https://inrix.com/

[2] https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4526796