1996 Chevy Silverado engine oil loss

I wasn't present when this occurred, but I was told that the engine shutdown instantly. What I found was engine oil all over the passenger side of the block (not from the head). This oil was mixed with coolant and was a thick brown sludge. I pulled out the dipstick to find very little oil but what was there was also thick and sludgy. I turned the key to find an engine that turned over normally, no freeze up. Could the head fail and over a very short time dump that much coolant in the oil and then dump the oil out somehow? Without cleaning up the mess it is very hard to see anything. This engine has always run perfectly and uses about 1/2 quart in 4000 miles. I use Amsoil.