No ones knows what was in the MCP window but they may have set missed approach alt, disengaged the autopilot and hand flown. Therefore no auto thrust and no flight directors commanding a level off, if they were switched on. Even off you completely misjudged the profile I can't see how the speed could get so low unless the auto throttle was either stuck in hold due to FLCH or had been manually switched off. My guess is the FLCH situation. If you had manually turned off autothrust, one would imagine you would pay a bit more attention to thrust levels. A misunderstanding of FLCH could lead to a lack of thrust quite easily. The ATHR push button on the MCP will still be illuminated indicating it is active, however it will not add thrust. As always, FMAs are king.