Is this "Boost" / File Manager app a true system app or malware?
This is a system app update from Alcatel. Recently they started updating some of their apps. I'm assuming you have an Idol 4 or 4S.

Although you can't uninstall or even fully disable this app, you can uninstall updates and stop automatic updates. Go to Settings - Apps - File manager. In the upper right-hand corner, push the three dots and click "Uninstall updates". Then go to Google Play - Your apps, click the file manager. Then in the right corner, click the three dots. Uncheck "Automatic updates". This will keep it from updating. You can do this with all of Alcatel apps.

I don't know why they thought having a purple octopus on the main screen a good idea but I and others have sent several emails regarding it and have been ignored.