Even if the 4 locking bolts (with their slotted nuts and cotter pins/split pins) were missing, the lower hinge arms which are still attached to the floor bracket, have a double lock nut arrangement on the shaft end and large washer, allowing the semi plug to rise and hinge outwards, spring assist, as it is apparently designed to do; the exterior fuselage does not appear to have any buffet damage from the plug assembly which indicates to be at least that either the washer was not large enough to hold on the bracket structure and the shaft just pulled through; Or the double lock nuts and washer was not present. Accepted the lanyards are unlikely to offer little resistance to the cabin pressure acting on the large plug surface.
I do not have a good definition screen to zero in on the hinge fittings on the outside to see if there is just thread or nuts present, anyone?