If the low limiter screw on the read derailleur was *very* badly adjusted, it would be possible to move the derailleur far too far past the end of the cassette by shifting into the lowest gear. This would move the chain off the top of the biggest cog and could force the derailleur into the spokes which, in turn, would bend it.

There's a lot of information on setting derailleur limiter screws on the internet - [here's a fairly good example](https://www.madegood.com/bikes/repair/set-a-limit-screw-on-a-rear-derailleur/)