"Orval Fairbairn" wrote

In the case of the firefighting plane, if it was flying level and
dropped a large weight (slurry), the wings would have the same load,
either with or without the dropped weight. Other airframe components,
such as engine mounts, fixed equipment, crew, however, would experience
a sudden increase in G loading. If the plane was flying at too high
speed, sudden updrafts/gusts could overload the wings.

My point is that the plane had a load and probably had substantial up trim
in, and full power, so when it's load was released with the power kept the
same, it probably zoomed into a climb, mostly on its own. The pilot also
very well could have pulled back on the yolk after the load was released as
is normal practice, to gain altitude. They have to drop very close to the
ground, so gaining altitude after a drop is S. O. P.

IIRC, the aircraft in question was an older C-130 and did not have the
proper, mandatory inspections performed on the wing spar box sections.

Sadly, also true. The fact remains that the wing was overloaded (for it's
condition) soon after release, though some combination of plane's
aerodynamic characteristics and pilot actions.
--
Jim in NC