I would have done the same thing- get under a desk or table, then leave until I knew it was safe to return. It's just common sense and established earthquake safety procedure.
I know exactly how you feel- I have many times been the only person to leave the building at work when there was a fire alarm. I have told customers that I was leaving until the alarm was over and that they might want to leave, too. Most employees and customers just go on as usual. A few months ago we had an alarm go off at work and I dragged my closest coworker outside with me. She kept asking if we were going to get in trouble for leaving our area unmanned. I told her I could care less what they thought and where I thought they could shove it, though I think it would be very bad legally for a company to insist that their workers remain indoors during a fire alarm.
I see people at the mall sit in the food court, feeding their babies strapped into high chairs as if nothing was going on, going into interior restrooms, etc. during fire alarms.
I don't play around. I was lucky to escape a burning building once (and only because I got up right away to see why the fire alarm was going off) and so I get the heck out of anyplace the alarm sounds. Personally, I have seen how quickly a fire spreads...it is better to be safe outside by yourself than to trapped inside of a building with everyone else before you finally realize there is a real emergency.