I hope you noticed he's been disconnected and placed under "Fictional Genealogy". He seems to have been a 15th century figment of somebody's overactive imagination, probably due to "folk etymology" - the same thing that gives us "sparrow grass" as a "folk" name for asparagus along with a folk tale that sparrows eat it when they're feeling poorly.
The FitzGeralds, aka Geraldines, were so called because they were descendants of Gerald of Windsor and his wife Nest verch Rhys - and they were proud enough of that not to need any gilding of the lily, thank you very much.
Gerald de Windsor, Constable of Pembroke