Right, it intentionally violates the URI spec by appending something to the end of it. The data structure they're storing has a natural pair-of-structures at its top level:

    data Database = InMemory | LevelDB Path | ViaHTTP URL

    newtype DataSet = DS Text
    newtype Hash = Hash Text 
    data Accessor = AccessDS DataSet | AccessValue (Either DataSet Hash) Path
    
    type DBAccessor = (Database, Accessor)

They elected to basically encode a DBAccessor above as a string which you can split on "::", with the URL above being stored on the left in the case of the ViaHTTP databases.