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They got spooked by someone at the point where they already had the QR off, but before they felt safe taking the wheel off the frame and walking away with it.

They were probably also using the paper to conceal what they were doing, and just dropped it when they walked away.

A long time ago some asshole undid my front quick release. I went to pop a wheelie off a curb and my front tire went rolling down the street and I ate shit when my forks dug into the pavement. I hope that dickhead got hit by a bus.

Lyle's expert analysis of the scene says a lot about him.