A pandemic is a large scale outbreak of a dangerous pathogen affecting a large amount of people over a large geographical region, or more precisely in several WHO regions. Typical features of seasonal influenza is small, gradual changes and some natural immunity. For pandemic influenza, we are talking about a global outbreak of a new strain that humans most of the time completely lack natural immunity against. Therefore, seasonal influenza cannot properly be considered the same as pandemic influenza.
As for your question regarding whether it is possible for a pandemic pathogen to only produce asymptomatic carriers, a lot of the time the symptoms created by the pathogen and the body's response helps to spread the pathogen, such as coughing, sneezing and so on. It can be considered a general rule that it is not likely that a pandemic pathogen would produce nothing but asymptomatic carriers. This is because pathogens that spread better than others will produce more copies of itself that can infect others, provided all other factors are negligible, so this type of pathogen would be selected for over time.