CONF iture;
The best that can be said regarding a slat/flap extension theory is, it is possible that such a selection was made at some point but improbable that it actually was. I think this because that is a significant operational emergency decision and would be noted in the IR3 even if the parameter has not been provided. There is no mention of slats and only one technical mention of flaps in IR3.
As Turbine D has quite reasonably asked however, of what significance is this in relation to the accident?
Vertical speed is a baro-inertial calculation. Inertial and Air Data systems have different advantages in the calculation. IR calculation is better in dynamic maneuvers and ADR calculation is more stable over time, (no IR drift issues). Input is automatically selected in accordance with reliability. If ADR data is unreliable it returns an "NCD" status.
Perhaps this may explain comments regarding behaviour of the IVSI display, perhaps not. Various data-source selections were apparently made (can't recall what they were, and also FCPC was switched off/on as well IIRC) - as I mentioned, system behaviours in these circumstances are much less understood than in normal circumstances and, like the earlier examination and sorting out of the ACARS messages, a lot of permutations/combinations would have to be examined before a definitive sense of what was being displayed on the PFDs at any moment during the post-apogee phase. The crew does comment on (loss of) altitude and rate of descent during this phase so something was displayed.