Marco's not crazy to think it's real at first glance, but your shadow test is the right move. The 3 different shadow angles are the giveaway though, not the shadows being present. One thing to check: slow the clip to 0.25 speed on your phone and count how many people in a row do the exact same arm motion at the exact same millisecond. Real crowds never sync up that clean, someone's always half a beat off. Also look at the edges of the frame, stitched clips usually have a person or rail that gets cut or warped where the loops meet. If you see the same section of seats repeat after 8 to 10 seconds, that's your proof. Tell Marco the $50 is late fees at this point.

Stud welders pull the easy stuff fine, but the old man's right that nothing beats a torch when the metal's stretched and needs shrinking.