IMR001 - There isn't a 'SINGLE CH' FMA annunciation on the Classic 737. 'Flare' wouldn't annunciate but thats a G/A from 500', not minimums - The likely response to the TOGA button being pressed then is a pitch up even if you don't touch a thing and the A/P drops out due to the pitch/power couple.
I don't think speculation will solve this one. The 737 autoland isn't the most advanced out there so the way forward will be the AAIB and the flight recorders...