I was looking for one as well, but it seems we did not write a blog post. I will do some digging when I find the time, as I know we at least messaged some people that voiced their frustration directly.
7 karma · joined July 10, 2015
At the time we weren't actually making money yet, and most of the contributions to Travis CI came from outside collaborators.
To add to the confusion, we did indeed have a bot in the early days that would comment on pull requests, but only if the repository was using Travis CI already (this has now been replaced by GitHub's status API). However, this was not the same bot account that kept opening unsolicited pull requests on random projects.