I would say water---not anti-freeze from the looks of it. --- either rain or lake water. Anti-freeze usually looks different when it goes into the oil,--like real nasty---this looks too clean for that-- gotta be just water.
Main thing to check next would be transmission to see if it too has water in it. --- I would suspect it was just rain got in the exhaust,---easy for that to happen even with a cover on the muffler/pipe.

"A machine you build yourself is a vote for a different way of life. There are things you have to earn with your hands."