Definitions of journalism tend to be more specific than this (I'll cover some aspects in a session on journalistic writing in week 3 in MED7370 which I'd encourage you to join!). For example politicans report on newsworthy matters in a professional capacity, but they're almost certainly not journalists, and influencers do too (they may or may not be classed as journalists).

Some of the key extra factors are the professional norms and values being followed in reporting on those, including their professional distance (politicians have a vested interest; influencers may be being paid to promote a product). It doesn't mean that a singer can't be a journalist, only that it requires more exploration.