I stumbled upon this paid app and surprisingly found that it has a cache cleaner feature and this contradicts what you insist on that is not possible on Windows Mobile.
It is a fake app. Many have repoted such apps. Just take a look at the negative reviews at the store. You can also check for yourself. The app will not be freeing any temporary memory. It only claims that it does.
As mentioned, such as feature is not possible via 3rd party apps in Windows 10 mobile.