Well, he's right - Kosovo IS monoethnic. The other ethnic communities have been murdered or terrorized into moving out/ethnically cleansed.
Kosovo became monoethnic when the native Albanians became 90 percent of the population, long before a third of the Serbs left in 1999. The Serbs left during the war of liberation, not after it. But they had indeed tried to expel the majority of the native Albanians.