You state, however, that you believe you did nothing wrong and will do the exact same thing again in the future and what you are sorry for is that the other person got hurt. I thought a "I'm sorry you got hurt by what I did" wasn't a real apology.

I'm just not seeing how this apology is in any way meaningful as an apology. Sure, change your actions with this particular person - we both agree on that. And sure you're responsible for hurting them if you do it again once you know. But I don't see how you even consider it to be a mistake when you go on to claim you'll do the exact same thing in the future when in the same situation.

It just rings very hollow as an apology and a belief in having made a mistake.

If there is some actual mistake here, then what is it and how can it be avoided altogether? I'm all for recognizing that this may be a common area of sensitivity. So, do you think you should always ask someone's pronoun choice before ever referring to them? What if you want to make a comment about someone in an online discussion who doesn't make their pronoun choice clear? What degree of research should you be obligated to do?