I would imagine that the sudden appearance of food and new environment elements would set the mind of any animal in a "run around and explore" mode, especially for species living near humans.
Also: the researchers hypnotize that the slugs ended up in the wheel by accident. Some mice returned multiple times; that's a fairly good indicator that they found some benefit from it (need not be that they liked it; it's fairly easy to make up perfect direct benefits. For example, it might be that fleas jump of a mouse if it runs in a wheel for a while.
My two cats are definitely more active when they've not recently eaten. When their food bowls are empty, they run around and play much more --- `hunger' tends to stimulate activity in them. Once they're fed, especially with something they really like and will gorge on, they tend to lie around and sleep after eating.