If it’s Someone whistling an on the fly melody then that’s fine. The musical work isn’t registered as being copyrighted. It’s just some bloke/lady whistling. So that doesn’t count and is totally fine.
If they were whistling a popular tune, well, that’s getting into the whole idea of arrangements. They’ve created a new arrangement of the musical work, which might be copyrighted. Depends on context with arrangements.
If this were a holiday video he shared with friends and family, it would totally fall under fair use. He’s not making money off the back of it.
As to all the other signs etc, no idea. My background is music copyright.