Hello, est15,
This question is more difficult than most Flaw in the Reasoning questions, because of the way the question stem is set up.
You correctly identified the Mistaken Negation present in the stimulus - well done there, by the by
- but the question stem is not a traditional one. Rather than asking for the nature of the specific flaw, which answer choice would probably look like "It confuses a sufficient and a necessary condition", it asks for a possibility, given the truth of all premises, that would show the argument's conclusion to be false.
Prephrasing is an extremely useful skill to have, but it will not work the same way one hundred percent of the time. Especially in the last five questions of any section, some questions are strange and unconventional, and standard prephrasing might not be as useful as it otherwise would be.
In this case, you would be able to prephrase by asking trying to figure out a possible scenario within the scope of the premises that would render the conclusion false. For example, perhaps the press agent told no reporter anything. Or perhaps the press agent told every reporter the exact same information, just not everything about the accident. Either of those is consistent with answer choice E and might help lead you to it.
This is a very tough question, but you're doing well. Hang in there!
Hope that helps,
Lucas Moreau