As the results show, the generic PBMT system outperforms its NMT counterpart in all the domains by a very large margin; and as the NMT system becomes more specific by observing more domain-specific data, the gap between the performances reduces until the NMT outperforms; which confirms the results of the previous works in this field (Luong and Manning, 2015).
it is interesting to see what is the reason behind the very low performance of the generic NMT system compared to the generic PBMT.