This page claims that this is not an ordinary error fare but a "special" one -- though what makes it special is not clear.

Perhaps it is that this airline (Royal Jordanian) has notoriously horrible reviews! Passengers question reliability, long and unexplained delays, hygiene issues and frequently report that crew members are indifferent and poorly trained. It seems much more likely that the airline is simply offering a low price in an effort to fill their planes. Caveat Emptor!