The history of launched game is stored in a file.
There were homebrew created to delete the file's content to hide the fact that you played homebrew.
multiMAN have this native feature too, whenever you launch multiMAN, that history is cleaned.
some homebrew let you add games randomly into it, to prevent always having a clean history for years (even more suspicious), but if you use multiMAN ontop of it, it will be cleaned anyway.
There were also a stealth method by using existing game ID for homebrew's ID.
As for online stealth to hide that you have a CFW, You can start by spoofing your fw version (to prevent being prompt to update, if you have an old cfw).
But it's only on your side, Sony knowns your real fw version.
There are program to rewrite your console's ID using FuckPSN or other tools as proxy, to prevent a console ban (doesn't prevent an account ban).
That was last year
I didn't follow recent events, but it tells you what was used long time ago to try being stealth.
But like said, there's no 100% stealth.
