When adding people to a chat, it shows the contact list from the device, with avatars. It is also possible to manually enter a phone number or username.
It's very likely that senior government officials have a phone with journalists saved in the contacts. It's easy to imagine why there are rules against using the same phone for secret war stuff, yet here we are.
That would solve the problem of accidentally adding journalists to chats, but phones belonging to high level officials are surely targets for the intelligence services of hostile nations. A phone that's used casually, taken to foreign countries, and not actively managed by security professionals is at high risk of being compromised given that threat model.
It's very likely that senior government officials have a phone with journalists saved in the contacts. It's easy to imagine why there are rules against using the same phone for secret war stuff, yet here we are.