Doesn't sound like what we would normally see for WHS symptoms. And with how common cancer and tumors are in these little ones, you are likely correct. However, you already know this, that you need to get a veterinary opinion and see if there is anything you can do to help his quality of life.
If his face/eye is swollen, I'd try to get him to see a vet sooner if you can. Could be very painful. I'd also likely try the canned food route just in case his eye/face is painful. Less crunching has to feel better right?