My son was recommeded nebulizer - albuterol because of congestion. Does frequent congestion mean he could be pre- disposed to asthma?

Congestion. Congestion could be upper airway or lower airway congestion. If lower airway congestion is associated with wheezing, it could indicate later development of asthma.
Could be. Making a diagnosis of asthma especially in young children can be tricky unless they present with recurrent wheezing and shortness of breath. Prolonged cough or frequent chest congestion could be an atypical manifestation of relatively mild asthma. I would recommend using albuterol inhalation, 4 times a day faithfully for a few days. Good response to the treatment confirms the suspicion.
Could be. FREQUENT CONGESTION AND WHEEZING COULD BE AN INDICATION OF BRONCHIAL REACTIVITY AND ASTHMA. Watch for signs of wheezing.
Maybe. Fully 60-70% of kids with wheezing issues in childhood grow out of it by school age. Albuterol is an anti-wheezing agent with little if any benefit to congestion. If it helps, there is likely some airway reactivity. Many viral illnesses have a wheezy component. It is also clear that some of these kids will go on to have some form of airway hyper-reactivity as adults.