Most likely event was a siphon occurred. I use a very low pressure cap and a catch bottle. If the bottle fills up I can see where it went. Nothing fancy, mind you just a plastic jug and some safety wire will do. But and this is helpful. When the bottle gets some in it the siphon effect is broken up and stops. If there is no water in the oil. And none in the tailpipe, I think this is what happened. And it is good to remember that steam will push a lot of water in a hurry. One bubble is all it takes. Did you have a weep/steam hole in the thermostat? Last place to look, is under the water pump pulley, if it looks like it was steam cleaned, it probably was. That is about the only other place to look at.
