I would probably not go that far. It is human nature to mourn. When my wife passed, I knew, deep in my heart that she was bound for glory in the arms of Jesus. That does not mean I didn't (and still do) feel sorrow in her passing. She is missed regardless because of the hole left in my life. I would imagine the same would have happened with his followers. Even if they fully understood what had happened, they would mourn. We mourn for ourselves more than the departed. It seems to be how we're wired, even when we know better.
It is human nature to mourn. .....Seriously, do you suppose mournfulness is because the death of another close to us reminds us the, the living, of the inevetible death where no one will remember us, never be blessed with ever knowing us we will pass on to oblivion? I think funeral rites only magnify this situation.