Alum shuffler:
If the photo is real, then altimetry error would explain the low altitude and the ADSB reports of being on profile as the ADSB would report GPS 2d position and baro altitude. Given how many non precision approach accidents have been caused by misset altimeters, it seems a plausible explanation, especially if the local QNH was below standard.
With all the publicity this incident has received, it's likely that the experts at Transport Canada will take a good look at the DFDR.