Yank the dipstick out, if there is coolant in the oil, it will be obvious.

We had a bad head gasket in a Pontiac 35 years ago and the dipstick looked like there was mayo in the oil.
Sounds to me like you just had condensation in the exhaust system. Deb Walker started her coupe up cold one morning and took off ahead of me, she sprayed steam all over behind her.