It was something along those lines, to do with chilled fuel (ie the fuel was cold rather than the tanks), which was able to be supplied. There was a thread aout this here recently.
In current F1, the teams are allowed a maximum of ambient -10C when refuelling, because there is a slight, but measurable advantage to pouring in chilled fuel!
Here's a link to an earlier thread:
http://www.pprune.org/tech-log/34873...l-density.html
SD