No. If coder of that bot is worked as they quite often do meaning there is some part of text in user agent, device, systen etc. that is same all the time then you can block them totally, but you need a reverse proxy. robots.txt is only guideline for good behaving bots.
Logs by Discourse are more or less just giving a blink of big picture. Such detailed data you must dig from logs of Nginx, meaning welcome console 
WordPress can easily go on its knees because of bots, but with Discourse the situation is more just annoying. Content stealing is today’s norm, and has been long time now.