I mean, magic is just weird shit that isn't fully understood yet.

That being said, you might as well look at it as branches.

Each state is a possibility, thus both exist.

The "magic" isn't that the probabilities of either state being in effect suddenly collapsed and became reality. The magic is that by observing the result, we collapse our own probability and are suddenly aware of the branch that we exist in. But we also exist in that other branch, suddenly aware that we exist in it. But "both" of us are incapable of viewing that other branch.

Which is all mumbo-jumbo, but I'm a fiction writer, so I don't have to be rigorous :)