The headline is slightly click-bait. Most the work is outside slack - parsing Craigslist, classifying etc.. The slack channel bit is one part of the puzzle. The article itself says there are 4 steps and devotes 2 paras to slack.
I guess the author chose slack in the title because it will result in eyeballs rather than saying how he used Python, craigslist because they aren't "sexy".
I found the work on classifying the results, sorting them more interesting. Posting to a slack channel as a bot today could easily have been a perl script bot writing to an IRC channel 10 years ago. That's hardly innovative. The really useful part to me was the access to craigslist, classification of data etc.. I'm sure there are better way of using Slack.
I guess the author chose slack in the title because it will result in eyeballs rather than saying how he used Python, craigslist because they aren't "sexy".