I don't think this date is just symbolic because of Executive Order 6102 and its abolishment. It seems like overthinking to me, so it might just be the day Satoshi was born. This person might have left this true date back in the times when Satoshi wasn't that popular, so there was no point at fully hiding one's identity up to the small details. So Satoshi, whoever you are, I want to thank you for your creation that's been truly revolutionary and literally changed the lives of dozens of millions of people who now use it. I hope you're alive and well, possibly even reading this stuff from time to time while staying aside and doing something else with your life.
That's a possibility. Perhaps it symbolizes something else that is more important that his Birthday? Maybe it was the date where he found something relevant to Bitcoin? who knows at this point. All this time, everything he does in the whitepaper has a meaning so I'm guessing that date has a pretty important meaning to it too. I doubt that date would be his birthday.