Single pilot it may have been but you have 2 experience pilots, both who would have extensive experience of company SOP's , even if the safety pilot was just a supernumerary on that day I would think he would be running through the SOP's himself anyway, they may not truly relevant as not tyoe rated but still relevant in this case of speeds.. maybe just maybe an event happened and a false positive or false negative proposition arose in which a true SP would have not been available too and just added to an already difficult situation..
Who knows, just a thought..