Is is just the annealing of the copper/aluminum process that makes it better to manipulate or is their a chemical/atomic reaction between the galvanized coating that is harmful to the tree.
The very reactive metal zinc will dissolve and be washed off with general watering, flushing high levels of zinc into the soil. The major change from high levels of zinc is in the nuclei of root tip cells. The chromatin material becomes highly condensed and some of the cortical cells show disruption and dilation of nuclear membrane in presence of 7.5 mM zinc. The cytoplasm becomes structureless, disintegration of cell organelles and the development of vacuoles will also occur. The number of nucleoli also increase in response to zinc resulting in the synthesis of new protein involved in heavy metal tolerance.
Somehow I doubt they were talking about leaching of zinc from wire into the soil. It reads like they are talking mine tailings, considering the concentrations.
Galvanized steel is used in a wde reange of gardening applications without any bad effects.
To me, the morelogical reason would be that the zing coating breaks, and rust ssets in, leaving stains on the bark.