Stock exhaust manifold is held on only by the bolts to the engine head and by rubber hangers to the underside of the chassis. There is no bracket and bolt which holds the exhaust manifold on, you'd get vibrations transmitted into the cabin otherwise.

Based on the rust, that is just something that was sitting on the side of the road for a couple of days.

And it was hot because of the sun. Can get over 50 ºC if metal sits in direct afternoon sun.