hmm, i dont really think his arms are very ripped at all, plus most figures that are obese have quite a bit of muscle mass behind it, so i think its reasonable.
His right arm, at least for my 2 cents, is SUPER RIPPED. He looks like the hulk. And while you are quite right that fat people or creatures can have a lot of muscle, it
is behind the fat. Meaning, it lacks definition! However, from where I'm standing, this is all irrelevant, I think the muscley arm looks quite good on this character! The only thing I would change as you move forward is you've put 5 or 6 fatty rolls into his otherwise very smooth looking belly, there on the left side of the image. They're shaded quite dark, and they're just reading as strange skin features, rather than fatty grossness (unlike the excellent pectoral highlights).
And, this may be irrelevant, but how did he get so fat without a mouth?
EDIT - mccow he already has one, how many does he need