See: Terms of Service - PyMC Discourse
Short answer from the link is that the posters maintain copyright to their posts, but license them to the site under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.
I’m not an expert on CC licenses, but the non-commercial aspect of this may be problematic. Usually share alike only kicks in when you try to distribute.
CC is generally considered a suboptimal license under which to distribute code, but I’m not entirely sure why. Here’s CC’s own take: