NA beer is not basically “beer flavored soda.”
The only thing the two have in common is carbonation and even that is produced differently in each. Soda is flavored syrup mixed with water that has been carbonated by forcing CO2 through it.
NA beer is brewed the same as regular beer, and carbonation occurs during this process. For some NA beers, fermentation is arrested before significant amounts of alcohol form, while others are subjected to a vacuum to lower the boiling point so that the alcohol can be boiled out with a minimum effect of the flavor.