The line should be agency. If they contribute to the action, and that is not forced some how, like self defense, they are not journalists.

They are actors.

Otherwise, people are journalists when practicing journalism.

Official press credentials? https://uspressassociation.org/

Also for some more direct on-the-ground reporting from events like this https://twitter.com/UR_Ninja is a really good, dedicated organisation.

Under the 1st amendment, every citizen is "the press" if/when they choose to be. No centralized credentialing agency required to prove it.