The mechanism behind metal whisker growth is not well understood, but seems to be encouraged by compressive mechanical stresses. According to Wikipedia.
Electrons in metal always move the same speed, and potential differences in modern high perf applications are never above 3.3V. There are mechanical stresses in ICs introduced during manufacturing. So these cases aren’t as different as you let on.
Anyway, point is, metal moves, we have some ideas why and can model some of them. From an engineering perspective these are both tin whiskers. We call whiskers made of copper and aluminum tin whiskers. You’re describing a distinction without a difference.