Every app on your machine creates cache files. They are used to speed up the running of the application. In your Web Browser, for instance, you will have a 'Refresh' (or 'Reload') button. If you click the button the webpage refreshes, no news there. But if you look at the button, when you press it the icon on the button changes while the process is running. If the app had to go back through it's own innards to find the icon for the new state it would take time. So the app makes a cache of such images for fast access.
In this case, all that's happened is that the app didn't clean up after itself when it quit. That's all.
They could be literally any app on your Mac. This really is a minor wee glitch and nothing to concern yourself about.
Regards
TD