I'd say the mist is coming from wind or rain hitting the tent and causing condensation to fall off inside. It's pretty normal with tents like the Rainbow that don't have a separate tent & fly. I try to deal with condensation by getting all the airflow in the tent that I can get away with without getting cold. You can also dab moisture that's pooled up by using a bandana or handtowel, which people often carry with them anyway.

Most modern sleeping bags come with a water repellant coating. How much this actually helps, I don't know.

There are a few things you can do to help with moisture after it's happened. I shake off all the moisture I can before packing it up, and if weather & time allow I'll sometimes pitch the tent during lunch so the sun can dry it out.

I used to get annoyed at how small items like glasses, camera, etc. would get moist overnight. Then I discovered that I could use my little raingear stuffsacks to protect my valuables. They get packed along anyway, and they work fine.