The reality is Border Patrol agents were purposefully shooting members of the press with rubber bullets and seizing their equipment regardless of their rights.
Just because there's some contrivance where an agent might justify this behavior doesn't mean they or their superiors won't be held in immediate contempt for violating this order. Judges aren't idiots, and this is about as harsh of a warning as they can issue before the case even gets finished.
And if that's seriously the standard they want to hold others to, then I think it's reaonsable to assume a random person in camo without any law enforcement ID on them trying to shove me into a van is a kidnapper and I should be legally protected in using violent force against them to defend myself.
When the standard is "know", it actually becomes quite hard to prove a violation. It isn't enough just to demonstrate that the fact is true, you also have to prove that the person who committed the violation subjectively knew it was true.
The text of the order says "reasonably should know". That means even if an individual federal agent didn't know, they can still violate the order if they reasonably should have known. But, what an individual agent reasonably should have known is itself a quite difficult question that can produce a lot of legal argument.
What if a federal agent is told by their superiors that "violent protestors are falsely pretending to be journalists/legal observers to take advantage of this order"? Even if the statement is false, so long as the agent trusts their superiors and genuinely believes it is true, they would fail to meet the "know" standard. (Knowledge is justified true belief, and if you don't believe it, you can't know it.)
Of course, maybe in such a case they "reasonably should have known" that what their superiors said is false. But how are they supposed to know that, and is it reasonable to expect them to know that?
Putting that aside, I think the US government is going to want to appeal. And if it makes it to the Supreme Court, whose side is the conservative majority going to favour?