The blog post regarding this “dump” suggests that it was actually from malware, so the answer to “Does that mean malware was once on your system?” is likely to be Yes. https://www.troyhunt.com/processing-23-billion-rows-of-alien-txtbase-stealer-logs/

Use the ‘Notify me’ option and verify your email address, and then it will show the expanded list of domains that were exposed from the malware: