I think you answered your own question - "maybe coincidence"?
Sort of like the claim one sees that "putting TUMS in the planting hole cured my BER".
There are far too many variables involved to give the PT wood any credit for the differences. At best, and in theory only, it "might" reduce the soil's fungus growth within an inch or so of the wood itself by leaching. But for the plants themselves, it could also be just the wind direction, or the sun exposure, or the shape and amount of the plant's foliage since it is possible to have one plant with EB right next to another plant without any EB.
Some fungicides are copper based, many are not.
Dave