The biggest mistake, forgetful moment, I see in the sim with cadets is forgetting to raise the gear either on a GA, or an engine failure, or turbulent X-wind. PF is fixated on flying and PM is fixated on what has gone wrong or not letting PF spear in. Problem is that all that drag makes whatever problem there is much worse.
I'm not suggesting there was such a scenario here, but it is so easy for attention to be diverted at a critical moment and forget to return to the normal sequence. Cadets being side-tracked, yes; well experienced line crews much less likely.