It seems the CVR would tell the story if all bleeds were off because at 10,000 ft cabin altitude high warning, if the same model 737 I flew, went off you get the takeoff warning horn as I did once. Outflow valve in manual or no bleed air would cause this but why would they continue to climb. The oxygen bottle would only be a factor if they continued climbing without rectifying the cabin alt high warning and ignoring the passenger masks dropping which seems highly unlikely. They should have been fine until over 20,000 ft before any hypoxia symptoms set in.