Nope, it's symbolism....Saturn talking trash about Humans being Insects in his point of view.
Furthermore we saw Luffy in Kumas flashback as he was practicing GUM GUM AXE.
So in conclusion how do people kill insects often ? They stomp on them isn't it?
Saturn is a spider like creature, ok Spiders aren't insects per se, the are arachnids - but you get what a mean I guess.
Saturn is an arrogant Gorosei, he describes people as insects. Saturns appearance ironically resembles an insect/arachnid. So it would be a fitting symbolism when Luffy stomps him.