First of all, you did great. Second, I 10000000% believe that it's ALWAYS better to call a code when you're not sure. I know you said you felt bad that it "wasn't a real code".. wouldn't you feel worse if it was and you didn't call it?
A couple of things I would have done differently- I would have skipped the finger thing and gone right to a sternal rub. If he was kinda out of it, a little bit of painful stimuli might have snapped him back. I would have also insisted that someone write up a code sheet, not just notes. There should be code sheets on your code cart I'm assuming? You did CPR, even if it wasn't for long. It's important to document that the patient became unresponsive, CPR was initiated, and patient became responsive again. Assuming the patient wasn't on tele and didn't have any other monitoring at the time of the code- it's impossible to know what exactly was happening when it started. Also, did you check for a pulse after you saw the rhythm on the monitor? Remember, organized rhythm doesn't always mean pulse.
I agree with the others that a debriefing would have helped a lot, but don't beat yourself up. It sounds like you did the right thing.