you did the right thing
Having flown the ERJ for several thousand hours i am fairly certain its not cold soak fuel that is causing the misting seen in your photo, it could be condensation or frost.
Some years ago i was travelling from ABZ on a BA Jetstream and due to a BA computer fault the flight was delayed by 2 hours it was early April clear sky and around 6pm, the crew had been on the aircraft with ducted air keeping them nice and warm, it was clear from my seat towards the rear that frost had formed on the wings, i wasn't sure if they were planning to be de-iced or not, anyway the door closed, so i showed the CC my ID and asked to speak to the Captain before he started the engines re a flight safety issue. I advised him of what i could see and he contacted the ground engineer who did finger tactile test on the wings and then told the Captain it would need to be de-iced!!
When i sat down the pax next to me enquired as to what had taken place and asked what i would have done if it hadn't been checked or de-iced, i told him i would have got off.
I have no problem with any passenger raising a safety concern, yes 9 times out of ten they will be wrong, but there have been cases where spolier pannel have detached in flight, at the end of the day its another pair of fresh eyes and not some that are half a sleep and seeing what they expect to see.