A few clues:
At the fwd inboard corner the flange is not damaged or displaced, therefore the screws were not in those holes.
None of the landings are damaged: if the screws were fitted you would expect the departing panel to rip off or damage the landings, or leave parts of itself behind.
The black bits trailing over the wing are micros witch harnesses for u/c indication/sequencing, which were attached to the inside face of the panel for support.
The fluid is probably fuel from a vent pipe or pressure sensing pipe also attached to a bracket on the inside face of the panel.
So the most likely explanation is that the panel was incorrectly / partially fitted