It doesn't seem to me like he asked for more evidence, but rather that he can't comment/discuss on something unless he's got the full context. The dude literally says as a response to someone wanting him to comment on it:

Comment on what? A picture of a headline?

What the fuck is there to comment on? Link an actual article that can be discussed

I read his comment as saying "I'm not gonna/can't discuss a single sentence, give me the full article and we'll talk." That seems reasonable to me. Is it not to you? He doesn't seem to ask for more evidence or anything, the second bit of his comment (The "You may actually be right") even shows that he's 100% willing to agree with the original person.

In all, it doesn't look like an "I don't believe it until I see the article" situation to me. It looks like a "There's really nothing to say about a single sentence. If it's true then you're right, but I can't/won't make a decision unless I have information."

I think that's a proper and healthy way to look at everything. After all, I think you and I can both agree that headlines are not always truthful and as a result it's good practice to get the full story (and ideally from multiple sources). What you suggest is that we don't do that when the story is about a cop doing bad. My question about that is: If reading the story before forming an opinion is what you do everything isn't it biased to not do it for "Cop did bad thing" stories?