I don't think its unreasonable to think someone might forget a rope. I also don't think it unreasonable to pick up said rope after a reasonable amount of time and try to return it to the party who forgot it. I actually think its a very nice thing to do and given the same set of circumstances as those described I would have (and have) done the same thing. I doubt any respectable guide service would intentionally leave gear behind at a crag to use the next day.
I do think its unreasonable to assume someone forgot a tent that was set up. Period.
Forgotten gear vs. Gear intentionally left behind.
Apples vs. Oranges.
YMMV