possible that the lower radiator hose on the right side could've squirted some coolant on to the front of the exhaust? Don't wanna scare ya but when my head gasket failed, coolant dripped on the AC near the front of the exhaust manifold. Like you, at the time I couldn't find where the frigging leak was coming from until one day, the mechanic put it on the lift and noted it was coming from an inconspicuous area in the head gasket... bummer.
If you don't smell coolant coming from the tailpipe, no coolant dripping from the head gasket on the exhaust side, car is not running rough or you cannot exceed more than 70 mph, then its gotta be something else more benign.