It makes it possible to prove that someone didn't forge a chatlog, but that you really said X at some point based on your friend's chat logs.
The article and/or its interpretation is wrong about that because the algo is unknown.
Even worse, human beings both currently and formerly employed by GOOG know the secret-ish algo, and those humans are not necessarily still employed there, nor are they incapable of communication. So its very unclear who knows how that algo works other than GOOG as an absolute minimum.
A correct statement would be, at the minimum at least GOOG knows how to make those hashes, and at this instant who knows how many other people or orgs who may or may not be in support or opposition to you.