Both mine do it also. It drives me nuts. They have two separate bowls and are in two separate rooms to eat ( I don't want Chloe eating Syd's food right now , we are trying to change her food) Yet they both do it. What's worse is the pieces of kibble they don't like they just drop on the floor and walk away from
so I have little trails of kibble leading away from the bowl.
I think it is just natural for dogs to grab some and go , like someone else mentioned "The pack mentality" get what you can and move away. Or maybe from when they were a pup's and had to fight for a place.