But as the article mentioned:

"Prosecutors in this case have stressed that they don't actually require the passphrase itself, and today's order appears to permit Fricosu to type it in and unlock the files without anyone looking over her shoulder."

So the state is arguing that they're not demanding the password, only the plaintext.

Still seems fishy, but it's not clear that it's testimonial.

I suppose one could argue that it's more akin to a judge demanding that you produce the corpse the police have so far been unable to locate.

Better still, as someone else said, it's like the police demanding that you translate notes you wrote down in your own made-up-and-known-only-to-you language.