I have had that as well and cleared the leading edges etc. And gone flying, after you got up a bit there was usually a temp inversion and the airframe became clear very quickly.
I presume it was cold air flowing down the mountains in the evening coupled to the warm air over the sea rising.
Whats more scary is on a cavok night flying along doing the xc bit of the night rating and it starts to form on the wings with no viz moisture around. I have had this a couple of times and decided I would prefer to be in the bar than in the air. So ended the flight as quickly as possible.
MJ