I'd have thought you couldn't re-roll Dump-Off either - or, rather, that you can't use a team re-roll to do so. Presumably you can still use the Pass skill to do so and that may be what you looked up.
I wouldn't beat yourself up over honest mistakes about rules though. We all make them and it can be impossible to correct after the fact (who knows what would have happened otherwise?). Good idea to bring it to your friend's attention, so one of you is more likely to remember in future, but you can't un-do what was done.