Sorry was a bit unclear, by two blocked domains I meant two domains in the original blocklist having the same hash, i.e. hn and adserver are both in our desired blocklist in your example
In this case only the one risk flagged in the article and other comments matters: that the hash of a domain you blocked coincides with the hash of a domain you want to access, so they are both blocked. There is no difference between false positive and false negative, it's all one collision leading to one unintended block.