Why do you think this?
>You can easily see how far the heat traveled simply by seeing where the insulation got blackened. It looks like just a few cm
Why do you think this? Copper is excellent at thermal conductivity, only beaten by silver.
> When electrical current flows through the circuit, the strip heats up due to resistive heating.
This picture [0] from post ("Toasted Wires") shows the temperature damage. As you can see, the insulation damages was only at the very end of wires. Most of the wire are intact, meaning only the very end heated up. The other picture [1] shows the same
[0] https://i0.wp.com/inthewilderness.net/wp-content/uploads/202...
[1] https://i0.wp.com/inthewilderness.net/wp-content/uploads/202...