If my cat is overweight after missing for one month, does this mean somebody had him?

My cat disappeared when I wasn't home and my careless 16-year-old niece left our bathroom window open. My cat was found roaming TEN MILES away from my house. Somebody saw him in their garden and turned him in, then the animal shelter contacted me after scanning for his microchip.
Update: My cat was 10 pounds before his disappearance. Now he's 14 pounds.
22 answers 22