I believe your reading is incorrect. The police are not allowed to order journalists to leave the area or to "round them up." The police were given a legal order by a judge not to do this. They did it anyway, issuing an unlawful order as applied to journalists.

If the police can't themselves operate within the law they're sworn to uphold, why do they deserve any deference or respect?

This is ultimately the question though. The Press is the so-called 4th estate of government. They provide information to the people about how the government (and it’s agents) operate. The police didn’t tell the press to disperse, they told the protest to do so.

So are the Press part of the protest? Are they impartial and there in an objective observer capacity only (can they be?)

I don’t know the answers to those, but it’s not hard to see police using this tactic to prevent press from observing and reporting.