Theoretically possible.....
Remember that water is denser than oil.... for the same volume,
muscle has more mass than fat.
I'm not saying I'm Arnie or anything.... but it's possible that
I've built up strong leg muscles from all that running....
Good point. I'm also very proud of the leg muscles I've built in
the last 6 months or so. My quadriceps look pretty good now but
need some work on the hamstrings to balance it out. 
