You must always also test the type of the variable to be boolean: VarType(varInput) = vbBoolean when using the Application.InputBox.
Dim varInput As Variant
varInput = Application.InputBox("Text", "Title", Type:=2)
If VarType(varInput) = vbBoolean And varInput = False Then
Exit Sub
End If
If you test only for False …
If varInput = False Then
… then it will also exit sub if you enter 0 or Falsch (in german Excel) or False (in English Excel).
This hapens because a string of 0 or "Falsch" (or "False") automatically casts into a boolean if compared with False. But only the Cancel button returns a true boolean.