Oh! That's probably an overstatement.
Let's simplify RPG play for the moment to in-character and out-of-character play.
In character, you use your speech and actions to directly convey your PC's speech, actions, and more generally identity.
Out of character, you talk about anything from your character to the mechanics of the game.
This is something of a canard in that it's impossible to draw clean lines between the two modes of play. If you hiccup when deeply in character, that's definitely your OOC body doing that, but you'll naturally present that as IC ... unless you're playing a robot or something, in which case you'll naturally shift OOC instead. And so forth. But conceptually, right, there's "here I am in the skin of my character, being my character in the medium of my words because they have no fleshly body of their own" vs. "here I am playing a game with y'all." as two distinct intentionalities towards play.
Because schostriches are devout, devout roleplayers---it's a cultural thing, I assume---they're strictly IC at all times in play. They say only what their character says. They act only in ways intended to convey their PC. It's obviously possible as real-world players to say "I flare my feathers to convey my rogue assuming an aggressive stance," but it felt to me like that was disrespectful, given that the schostrich was explicitly trying to convey not "look at me and my feathers" but "my rogue is assuming an aggressive stance." It felt like it was a way of demeaning scholarly ostriches to allow players to do that. Does that make sense?
But all that really does is say, you're not allowed to step into your character's skin without stepping into their character's skin. You're absolutely still allowed to talk OOC about your schostrich, and you're absolutely allowed to let it impact how you play. How could you do otherwise? If your rogue's an elf, that impacts how you play them even when they're not saying poser things like "as an elf, I flare my ears aggressively." If being an elven rogue didn't affect what they did then you might as well not be IC at all. If being a schostrich affects nothing then you're already playing your character as if a schostrich, which seems an overstatement too.
I do think that in a lot of gaming people go sort of halfway IC. They use inherently OOC techniques to express their character. For instance, giving a voiceover as a character when the implicit idea that they're telling the story to someone in the future is not viable. (There's also the flip side, seeking OOC objectives through IC means, but while that's usually good play it's also logically impossible.) Half-IC play gets tricky because---well, to take the example of a voiceover, it's clear that a schostrich looking back and telling stories of the campaign is probably not playing a session at the time and therefore able to mention things like feathers, but at the same time, that requires them scorning and reinterpreting their past self in the same cruel way the rules of the Schostrich Colocation ask you not to. Is it reasonable to imagine that in the grim future of the schostriches they become bitter and disaffected and no longer love roleplay and so dedicate themselves to ripping the mask from their past self and narrating roleplaying stories in their schostrich identity? Is it reasonable to step out of character and then begin to narrate a voiceover in that embittered schostrich voice? Well, technically, of course it is; you're out of character and as history shows people who are out of character can say literally anything. But perhaps it bends the spirit of the game.
Anyway, I guess all I'm saying is that if you believe playing a schostrich (struggling perhaps with a midrange malark) playing at being an elven rogue, mech pilot, youkai helping small-town humans, or you is the same as just playing an elven rogue, mech pilot, youkai helping small-town humans, or you yourself then the colocation in fact brings nothing to the table for you and perhaps your group. But inevitably one must accept that if this is so you are functionally playing a schostrich playing a dedicated elven rogue roleplaying yourself at all times and Marcie of Dark Dungeons fame was correct to fear Black Leaf's demise.
Conversely, it must be admitted that---even if you accept this argument, and agree that the colocation makes a meaningful difference in your play---the game is v. 0.1 because it was written between 3 and 5am and therefore the added fun value of the additional layer of play cannot yet be guaranteed.