That demonstates something that I have suspected but never proven. Chlorine does burn gills and soft flesh but it is not the instant harm we often think of it being. That brings back the old discussion of whether we need to treat water before, during, or after water changes. Seems to me with the number of people doing it each way and what you found, I think chlorine is less a danger than many think. Short term exposure, even at high concentration is not instant death.
You did do a big NO! NO! even for me!