I think Monotone was an alternative to BitKeeper and BitKeeper was the inspiration of Git and Mercurial. It even seems to suggest that in the link you posted.
BitKeeper not being available anymore was the impetus for starting Git and Mercurial (as replacements for BK), but many of the concepts in Git and Hg come from Monotone, most importantly the use of merkle trees (according to /u/ggherdov Matt Mackall[0] recently mentioned this explicitly on IRC). Linus also mentioned Monotone by name as "the most viable alternative" before starting/publishing git[1] and as pgeorgi noted contributed to the same.
http://www.monotone.ca/monotone.pdf
https://en.wikipedia.org/wiki/Monotone_%28software%29#Monoto...