And you expect not to get a variety of answers from a internet message board
I'll start the speculation - and try to get a ADAs opinion on it a little later.
I say if this friend was not read his Miranda rights then he was not arrested.
Disclaimer: EVERY STATE'S LAWS ARE DIFFERENT
USMCFLYR
Update (Immediate)
I went ahead and called and found out that I missed this question on the law test
1. Your friend was let off with a warning. The legality of it being a concealed weapon (like my disclaimer above) depends on the state's statues.
2. When review by the DA, he decided to file charges / a warrant.
3. At this time, your friend was under arrest.
4. When he went in, he basically turned himself in instead of the warrant having to be served on him. This situation has a name but I forget it now.
Thankfully, the judge seems to have seen it for what it was and dismissed it, but it sounds like technically he would have to say "yes" to the question and have an interesting story to tell. Btw - the ADA I called said that they wouldn't charge in that situation. Sorry about the "small town" situation
USMCFLYR