Fuel in the filler throat

I was outside and smelled diesel, and started to investigate. Long story short, I discovered in the filler I could see fuel. It (apparently?) expanded from the increased heat of late, and leaked out the filler. I found no signs that it dripped or ran out, just leaked. I checked this morning, the fuel was further back from the throat, closer to the tank.

My question is, am I likely correct in my assumption that it had expanded from the increased ambient temprature? I take my coach on monthly runs to a truck stop 30 miles out, fill, and return. I filled until I saw fuel spit out, and I had to use 5-6 gallons on the way back. Due to winter, temps have (until recently) been pretty chilly.

Thoughts?