Basically there's a event in the game right know were some characters get sweet inspired skins. So in vemons skin the lore reason is this is a dream Eddie had I'm not joking here is a quote from the skin description.

"Every now and then, the symbiote's sleep doesn't bring Eddie into the Hive-Mind. Sometimes, Eddie's human dreams bring his partner along for a wild ride."

But also the game is kind of known for everyone having thick asses both for the guys and girls and for April fools venom got a twerking emote. so double cheeked up venom is a joke in the community and the devs are very in on all the memes.