'Jet' has been used to describe many different types of propulsion system. The first jets were what you'd call rocket engines. Then we got 'turbojets' (mostly o

'Jet' has been used to describe many different types of propulsion system. The first jets were what you'd call rocket engines. Then we got 'turbojets' (mostly on aircraft), followed some time later by 'turbofans'. Most confusingly, ducted propellers on submarines are called 'pump-jets'. I would agree with you that this seems better-described as a ducted fan (which the author also says), but this use of 'jet' is not beyond the pale.