Why some of the accounts listed as inactive had tweeted a few times?

We refresh our cached data every 15 days. That means the data you came upon Circleboom couldn't be older than 15 days. We try our best to display the most recent version of the data on the search results (grid); however, it may be as old as 15 days.

On the other hand, our "inactive accounts" algorithm creates great results with cached data of Twitter followers and gives accurate results. If you check these accounts, you would see that most of those accounts are inactive, which means they aren't tweeting frequently even they have new tweets.