Well if, to have silver pied, it requires that a bird carry one pied gene, one white gene (both alleles) and two WE genes (homozygous for WE), then the "dark pied bird from silver pied parents" is not exactly "hiding" silver pied genetics. It just happened to get two pied genes (one from each parent) and should also have received two WE genes, one from each parent. So that "dark pied bird from silver parents" probably is White eyed in addition to being dark pied... and because of the two white eye genes, it might show more white than a dark pied with no white eye genes, a so-called minimally-marked pied.
The white birds from silver pied parents (also 25% of the offspring) will be carrying two white genes (one from each parent) and two white-eye genes (one from each parent). Those white-eye genes will be "hidden" by the white coloration of the entire bird, so there won't be any way to visually tell that the bird is carrying the WE genes.
But if that white, double-factor WE bird is bred back to one of the dark pied, double-factor WE birds, then all of the offspring should be silver pied... because they will get one white gene from the white (homozygous) parent, one pied gene from the dark pied (homozygous) parent, and one WE gene from each parent, since each parent is also homozygous for WE.
The problem with the reasoning "blue pied can hide silver pied" is that it compares apples and oranges and gets grapes. "blue pied" is either referring to a bird carrying a pied gene, or two pied genes, or a white gene and a pied gene, and we don't know which. Silver pied appears to require a combination of genes, of which, the "blue pied" would at best be only a part.
And yes, the quote does only mean that both the white gene and the pied gene can EXIST with other patterns. It does not state what the outcome will be in any given case or with any given pattern, because to know that, we need much more information about the specific bird and its parents.