Seems to me they tend to defer to the categories of others.
That is, it’s not usually the news media determining someone is in “serious” condition – it’s the hospital they ask about it. The media generally just reports what the hospital said.
Or it’s the police. Again, the news reporters generally just say what others say.
If they have to go by their own eye-witness assessment (which is rarely the case), they’ll refrain from speculation or they’ll say something like, “It looked to me like he was probably pretty badly hurt…” or something.