Under normal circumstances, the "not following back" page shouldn't show the accounts you are currently following. This issue is related to Twitter Discrepancy and happens rarely. Most likely, the issue will disappear on your next log-in to Circleboom.
We are directly getting the data from the Twitter APIs and listing them as is. On the other hand, Twitter APIs might send wrong data rarely. That is a known issue for the accounts that make aggressive follow and unfollows on the Twitter ecosystem and called "Discrepancy." Twitter’s back-end systems run on a distributed cluster of decomposed services. There are often cases where data sets will need to resynchronize between instances and data centers. This means, all the user data moves between server farms all the time, and some data servers may update later than others. (It is also a common issue among the Twitter community here: https://twittercommunity.com/t/discrepancy-in-followers-count/80018/20)
To prevent this behavior, we always suggest our users act less aggressively, as Twitter strictly mentions in its policies and rules.