It's not just about appreciating and respecting it though, that's fair enough.
He's asking people to remember to refer to "Sam Smith" specifically as "they or them", rather than 99.9% of the rest of the population that aren't offended be referred to as "he or she", lest they unintentionally cause them (Sam Smith) embarrassment or emotional distress.
Again, this isn't an attack on thier (Sam Smith's) decision, just simply pointing out that most people will totally forget to do it without intended to cause offence. Hell, I made about four "errors" typing out this post that had to be corrected.
It really is getting trickier and trickier to play by the rules these days.
Edit: Reading through the rest of the thread I've literally only just noticed that your post referred to Sam Smith as he and not they. See this is what I'm talking about! It's a minefield.
One, that's a bullshit percentage. Two, it'd be difficult to actually get an accurate percentage because being non-binary is so stigmatized and misunderstood that it's often difficult for people to both come to grips with and decide to come out about their own experiences with gender. Three, the way you've framed this post is actively hurtful. You think having to remember peoples' pronouns is a minefield? Imagine actually being trans. Imagine innately knowing your own gender, wanting nothing more than to be accepted as you are, just so you can go on living your own life. You never know who's going to accept you, not even your own family or friends. You have to weigh your options every time you even think of being honest about yourself with people, because if you choose the wrong person to trust, they can make your life a living hell. You decide you wanna go fully public with your identity, like Sam did? Now you've exposed yourself to the internet trolls as well, who can and will take every opportunity they can to scream at you about how little they acknowledge your existence. You log into Resetera and open this thread hoping to see some support for a highly visible person coming out themselves, only to be hit with a wave of posts denying the validity of they/them pronouns, and posts like yours bemoaning how tricky it is to live in a society where trans people exist.
Needless to say, being trans is a hell of a lot tricker than your situation, so you'll have to forgive me for not feeling much sympathy. I get that nobody's perfect, mistakes with pronouns happen. But next time you catch a mistake while writing a post? Just fix it and move on. Believe me, we know plenty of people are gonna fuck this stuff up, we really don't need to be reminded about how seemingly hopeless of an endeavor it is.