Regarding the possibility of setting-up a manual inserted approach into the fmc, let me give this theoretical possibility:
crew initially planned for an approach on rwy08, which is logical as this would be the preferential rwy according to current wind in the metar/atis, and had to change last minute for a setup for rwy26.
Runway and/or approach not in fmc database, manual entries in fmc. This caused the crew to be rushed.
As the aircraft showed problems with capturing ILS signals on previous sectors, which was not put in the techlog, (something that is a common occurence with ACT by the way), they followed a LNAV/VNAV approach, with a vnav path based on last point in fmc: threshold rwy08 where VNAV calculates to fly over at 50' .
This is by the way a rumour "on the ground"...
Totally unbelieveable obviously, but theoretically possible and an explanation that correlates with current information.