It still shows up as "tweet unavailable" for me, though, in this link

What you're seeing is an available tweet with an embedded tweet that is kept from being displayed. Because the embedded tweet is itself, it is handled by showing the same UI as any embedded tweet that is not available.

Right, but my point is the behavior is the same on Twitter and nitter

"tweet unavailable" is a different error from the "This is not available to you" message. Got that message earlier today when I tried to open a different linked tweet. Changing to nitter fixed it for me.

Ah, I get tweet unavailable from both, thus my confusion.