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The article does a lackluster job of explaining this, but the body schema is very different. Body schema is not about making adaptations to an environment, such as the experience of "sea legs." The body schema is essentially the concept of the body, and what it encompasses. Essentially, it defines "where and what is my body?" The answer to these questions -- and therefore, defining a body schema -- is not as straightforward as it seems. That debate can happen elsewhere. However, one part of the answer to the "where is my body" question is partially answered by proprioception, which is arguably part of the body schema. Proprioception is the mostly unconscious awareness of where your body is in space. It is what allows you to walk without looking at your legs, or touch your nose with your eyes closed. This leads to the point the study attempts to make.

The important part of the study, here, is that proprioceptive drift is experienced after people use tools. Again, the article doesn't explain this very clearly, but the point is that after a person has used tools, the locations or points at which the person's body ends and the tool begins become blurred and the tool becomes "a part of the body". As a result, after using the tool, even when it is not present, a person's proprioception, or "awareness of the body's physical location in space" will be slightly "off", as it had come to include the tool. This is not muscle memory, etc., or experiencing "sea legs", which are adaptations to an environment. This is, instead, the incorporation of a specific, and foreign, object into the body's proprioception. However, whether or not this constitutes actually becoming a "temporary body part" is debatable, I think.