Worded as such it does appear threatening. If someone tweeted that about me I would feel worried about my personal safety and that of my family. The law specifically states that placing a reasonable person in fear for their safety via online communications is a crime.
If you're going to request personal information for a legitimate reason then you should word it in a non threatening manner.
"...it's also a request to identify a police officer, which has legitimate purposes."
And given the context of calling a police officer a "bitch", do you think the requester was doing so to accurately file a complaint... or doing so in the hope that armed with the cop's identity, somebody would engage in harassment of that man and/or his family?
Being charged with a felony for the tweet is absurd.
But painting this as an innocent request for information is almost equally so.
"Identify this public servant" isn't against the law. I for one want strong third party oversight of our police from the public and from journalists. Police should be identifiable and although they didn't phrase it very nicely, the request isn't illegal.
Unless you think that calling a police officer a bitch is a felony.