Understanding why a process is unstable

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I am trying to understand what they are doing here to demonstrate instability:

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I know that to demonstrate that this process is unstable, I must take a sequence $\{x_n(t)\}_n$ such that $x_n(t)\to x(t)$ and see that the corresponding output values ​​$\{y_n(s)\}_n, 0\leq s\leq 1$ converge not to $y(s), 0\leq s\leq 1$, but in this example do the opposite or is it my opinion. Could someone explain to me please?