You're not, the person you're replying to was. I find it odd that you would object to an analogy where the signal propagates through the marbles at the speed of light (i.e. 'instantly'), and offer up instead one where each marble moves simultaneously. If the exit event is simultaneous to the entry of the other marble, they are separated by a spacelike interval despite the causal relationship between the two events. This violates relativity.
On the other hand, in the original analogy the two events are separated by a lightlike interval, which while impossible in the case of marbles, at least does not violate relativity when the two events are causally linked. This is what I meant when I said the conflation of the speed of sound and the speed of light is not such a big deal, in this case.
On the other hand, in the original analogy the two events are separated by a lightlike interval, which while impossible in the case of marbles, at least does not violate relativity when the two events are causally linked. This is what I meant when I said the conflation of the speed of sound and the speed of light is not such a big deal, in this case.