Processing is ANYTHING done to food.
So cutting, mashing, grinding, cooking, smoking, pureeing, boiling, etc.
Those are all processing of food.
An unprocessed food is say...a whole, raw apple.
ALL processing damages nutrients, although some more than others. A whole, raw apple is much better for you, than say applesauce. Exactly how that applesauce is processed also makes a difference.
A whole grain of wheat is MUCH more nutritious than the white flour that is made from it by processing.
So...yes, smoked salmon is processed, but it isn’t processed as much as some other foods.
Most food that we eat is “processed” somehow, but some foods are processed more than others. Most of the time when the term “processed food” is used, what is being discussed are HIGHLY processed foods like refined wheat, refined sugars, cured, meats, etc.
One thing I’d be concerned about with smoked salmon is exactly what sort of additives and chemicals are being used for it and what sort of smoking process is being used. I have had access to excellent homemade smoked salmon most of my life, I know exactly how it is made and it makes most other smoked salmon type products pale by comparison.