It sounds like the fish were brined in a dill brine before smoking.
Keep in mind that the "Big Chief" (and "Little Chief") are designed as a flavor enhancer, or pre-smoker before going into a hot smoker or into an oven. Essentially it is a cold smoker. The temperatures inside the Big Chief / Little Chief smokers runs about 140° to 150° depending on the warm weather outside, and even substantially lower when the weather is cold.
They're simple, They're hardy, and they can get the job done. Hard to beat for smoking cheese, nuts, spices, fish, or jerky. They are basically designed to be used as a flavor enhancer / cold smoker as long as you don't try to exceed their capabilities (Volume and Temperature) they work do fine.
The "Big Chief / Little Chief" smoker will not produce large amounts of the thin blue because of it's limited size. The only combustible materials are your wood chips which burn in the wood chip tray by the heating element. When wood chips first ignite they will give off white smoke (normal for electric smokers) until they turn black and appear like little bits of charcoal. At that point you will have your invisible thin blue smoke until they turn to nothing but gray / white ashes. You cannot see the "Invisible Thin Blue Smoke" unless you have the perfect angle of light. Use you nose, if you can smell smoke it is there, if not then you can add a few more chips into the tray.
Never completely fill the chip tray with wood chips, scatter them about and leave about 50% of the bottom of the tray exposed. When your wood chips turn to 75% ash, you can then add more chips, repeat this to keep the smoking cycle going.
Fish like salmon, have it's own delicate flavor, so you don't want to over-power it with a strong smoke flavor, nor do you want to use high heat to cook it relatively quick before it can absorb the cold smoke flavors imparted into it. Lastly is the type of wood you smoke with, don't use a heavy smoke flavored wood like hickory or mesquite. Alder is probably your most preferable choice, but a light fruit wood like apple in smaller quantities would also work well.
The type of cooker you use makes all the difference in the world for your finished product.
You can achieve cold smoking the salmon with the A-Maze-N pellet smoker in your current smoker without any fire in the firebox. The next step of cooking will depend on the type of smoker you have, a stick burner may get too hot, so maybe using an oven to finish it at a lower temperature of 150-160 might be a desirable alternative to cook the fish.
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