i'm thinking it was air in the cooling system. I started the engine from cold with the radiator cap off to flush the air out. i squeezed the upper radiator hose a few times to make sure i got it all. I've driven it maybe 20 miles since then with no problems.
I am thinking it was probably a steam bubble just because off how fast the temp went up and then shot back down, presumably when the bubble got past the temp sensor.
we shall see.....