As soon as I read the city (Gdansk, known to me from my boyhood interest in WWII as "Danzig"), I wondered if or how he'd have been involved in the shipworkers' activism, which ultimately overthrew Soviet communism and (s)elected a pope. Reasonably people can argue about what part they played, but I don't think anyone would deny that they had at least some hand in it.
Adamowicz was part of the democratic opposition formed in Gdansk under the leadership of Lech Walesa during the 1980s.
It's mightily wrong and (stochastically terroristic) for the ruling Polish Right or their supporters to call him a Nazi. Unfortunately, I have nothing much more to add to others' comments of condolence, sadness, fear, and concern.