Will this plumbing setup result in galvanic corrosion?
Looking at your photo I believe I see the upper 2 pipe unions appear to be dielectric unions, notice the orange insulators.
Dielectric unions isolate the copper to steel and would be the industry standard way to connect copper to galvanized pipe.
The lower pipes are flex pipes most commonly nickel plated brass with a plastic liner so no problem there either. It appears if anything the wrong type of nipple was used those fittings are for compression type not pipe thread thus the most probable reason for the leak. And the mass of Teflon tape that they tried to seal things with.
Ball valves can get sticky due to contaminates in the water (no corrosion statement would point to this) even the cleanest water and non use of a ball valve can cause a failure.