I think that would be just for eye candy and nothing else. HE rounds/rockets exploding externally of a heavily armored tank like the tiger wouldve probably dent the metal and maybe blow off a couple of bolts/plates. If you wanted to hurt the tank, you would have to hit its track/the ground near it, tracking it and/or killing the MG gunner.
While it IS weird that rockets "richochet", IMO, it's not a big deal. And it doesn't happen often enough for it to become a glaring oddity.
The only way I can think of a HE rocket killing a tank like the Tiger would be a one in a million shot through the turret hatch/driver viewhole. You can certainly damage the thing, engine, track, MG gunner, but I doubt you can kill a tank with rockets alone. (PB1 excluded)