No no, it wouldn't offend, because there was no actual french people around, and Fingon mimicked the laugh perfectly! It was a dastardly laugh, fueled by the prospect of adventure and robbery. Not to mention, if Maedhros' was rapidfire french, then Fingon's was french on helium shot out of a space cannon at lightspeed. With glitter.
"We cannot do worse, for we are noble robbers, and we don't accost women on the roadways! Unless it's to steal their fancy purses to put our coins and jewels into. And their jewels." Because those counted, too.
Fingon too eyed the stick robot unicorns, like EUREKA! NEW MOUNTS. Too bad they didn't have real legs, but there was a strange squeeing earbleeding sound in the background, that pretty much heralded the arrival of yonder harpy.