To sniff and to smell, they are basically the same thing right?
Actually, sniffing and smelling are two different phases of the smelling process.
Sniffing is defined by air rushing up your nose, while smelling itself begins when the odorous molecules attach to nerve cells in the brain. Scientists have discovered that while sniffing uses one part of the brain, smelling itself uses another part of the brain. Because there is some overlap in the areas of the brain used for the two phases, it is believed that sniffing somehow prepares the brain for smelling.
While your nose muscles certainly help you to sniff, movement of the nose muscles alone does not trigger the sniffing part of the brain.
For instance, if your nostrils are blocked due to congestion from a cold, it doesn't matter how much you attempt to sniff, the part of the brain that operates during sniffing will remain inactive.