Being skilled in one area doesn't make one an expert elsewhere. .. a rather dramatic example.
Fomenko is a supporter of drastically revising historical chronology. He has created his own revision called New Chronology, based on statistical correlations, dating of zodiacs, and by examining the mathematics and astronomy involved in chronology. Fomenko claims that he has discovered that many historical events do not correspond mathematically with the dates they are supposed to have occurred on. He asserts from this that all of ancient history (including the history of Greece, Rome, and Egypt) is just a reflection of events that occurred in the Middle Ages and that all of Chinese and Arab history are fabrications of 17th and 18th century Jesuits.
He also claims that Jesus lived in the 12th century A.D. and was crucified on Joshua's Hill; that the Trojan War and the Crusades were the same historical event; and that Genghis Khan and the Mongols were actually Russians. As well as disputing written chronologies, Fomenko also disputes more objective dating techniques such as dendrochronology and radiocarbon dating (see here for an examination of the latter criticism). His books include Empirico-statistical Analysis of Narrative Material and Its Applications and History: Fiction or Science?.
a tip of the hat to Bjarne