Yes a person can be big boned but it is quite not as common as we think it is and most people that claim they are "big boned" are usually just fat. I'm fat myself even though I have big muscles too but I am certainly a fatty. Honestly only a doctor who can do the right examinations will be able to say you are fat, muscular or big boned but you can always compare your wrist bone with others, pretty much the only bone that will still stick out even though someone is fat.