“Thinking about this.You were not found guilty, but nor were you found 'not guilty'. “
No, you would not have been found either guilty or not guilty. Assuming you did not face a trial (where you would have been declared Not Guilty) it is probable that the prosecution “offered no evidence” in return for you accepting to be subject to the Restraining Order. If the charge was withdrawn then it is as if it was never put and your status (being either guilty or not guilty) is the same as mine in relation to the same allegation.
I think that the reason for the RO appearing under the “convictions” section of the DBS report is, as has been mentioned, that there is simply nowhere else to put it. It is quite clear from the wording that you have not been convicted and this should be obvious to anybody reading the report.