The authors analyse the occurrence of "pertinent keywords" found in Google Books from the period in question. As far as I can see from the abstract, the keywords are selected on the assumption that capitalism can be associated "with any form of over-average importance or even dominance of the economy" .
The argument appears to be that an era is capitalist only if people are strongly conscious of the economy and of certain economic phenomena, and that this consciousness is reflected in the literature of the time.
This doesn't allow either for the possibility that people didn't talk about capitalism because they took it for granted, or for the possibility that they were suffering what Engels called "false consciousness". (Marx is often credited with this concept, but he never used the term himself.) Foucault showed how the Victorians thought differently about certain things (such as discipline and sexuality) but that doesn't mean those things didn't exist.
It is also worth noting that the literature that is preserved in Google Books may not fairly represent different social classes. As Ruth Livesey comments in relation to a different collection, "although there is much to be learned about middle-class life ... relative few that give central place to class".
What about the reverse argument? The religious authorities were obsessed with witchcraft between 1550 and 1700, particularly in Germany and Scotland, and King James VI of Scotland wrote a treatise on witchcraft. So if we analysed "pertinent keywords" (not to mention the "necessary hashtags"), we might be able to "prove" that witchcraft was more prevalent than capitalism in this period.
However, as @kvistgaard points out ...
Evidence-based policy leads to policy-based evidence. Then and now.— Ivo Velitchkov (@kvistgaard) January 7, 2018
Twitter is not an appropriate place to seriously discuss concepts like "existence" and "truth".
Yasmeen Ahmad, How Much Of Data Science Is Witchcraft? (Forbes 5 May 2016)
Jamie Doward, Why Europe’s wars of religion put 40,000 ‘witches’ to a terrible death (Observer 7 January 2018)
Barbara Humphries, Nineteenth century pamphlets online (The ephemerist, 153, Summer 2011).
Daniel Little, False Consciousness (University of Michigan-Dearborn, undated)
Ruth Livesey, Class (Oxford Bibliographies, March 2011)
Steffen Roth, Vladislav Valentinov, Arūnas Augustinaitis, Artur Mkrtichyan, Jari Kaivo-oja, Was that capitalism? A future-oriented big data analysis of the English language area in the 19th and 20th century (Futures, Volume 94, November 2017, pages 1-84)