Welcome to the '(e) check' club. Sounds like you could have prevented the process if you paid heed to the speed limit, but Im glad it all went smoothly.
With the recorders that are available these days, it really isnt necessary to leave it off until you need it unless you prefer to keep your audio 'private'. Just turn it on and let it run until you are to your destination with your liberties secure.
While they may have stepped over the line in recording your s/n, the duration didnt deviate much from a typical traffic infraction- so no foul there.
It appears that this was a pretty neutral encounter. Nice job.