No, I would not take that as evidence that God existed, I would take it as a paranormal phenomenon, since that could never happen under normal circumstances....
It would never happen unless God took over human free will and made it happen, so indirectly it might be evidence that God exists.
As
@Sgt. Pepper knows only too well, there are paranormal things that are inexplicable by any known scientific understandings. Would that do it for you?
I would not hold your breath waiting for that to happen. Elimination of all disease would require God intervening in the natural world and overriding the course of nature and removal of all the weapons would require going against the laws of physics!
But that still would not prove that God exists since it could be caused by aliens as you said. Aliens who were much more advanced than humans could make diseases disappear and they could locate and grab up all the weapons. Just think about what we can do now that we could not do 50 years ago, GPS and all the other technology we have. There is no end to what humans can do if they set their minds to it. We could even find the cures for all diseases so everyone would live into old age and die a natural death.