How to quit an app in OS X Yosemite
Your last screenshot is showing the apps that were running in the past 8 hours. You can try running ps -e | grep -i bittorrent in Terminal.app to confirm, but it doesn't appear to be running at this time. Relaunching the Dock should make the icon disappear, unless it's a side effect of autotermination:


  In Lion [and subsequent versions of OS X], an ostensibly "running" application may have no associated process (because the operating system automatically terminated it in order to reclaim resources) and an application may have a process even when it doesn't appear to be running. Applications without processes. Processes without applications. Did Lion just blow your mind?