Something that works in the artist/album/track format has no need for it, and something that doesn't adhere to the composer/orchestra/recording/etc format of metadata and organization that classical uses, also doesn't fit very well.
Classical film scores are definitely good fits, because they have composers and there exists multiple recordings done by different orchestras and so on.
It may be that some categories of music that aren't traditional western classical will fit right in, and might be put here instead of in the regular Apple Music, who knows. But mainly, this is just a way of finally recognizing that Artist/Album/Track doesn't work and never worked for classical, so it's a way of correctly organizing/browsing/consuming classical music.
The question is not “how do we draw the line between classical music and non-classical music”, but how do we fix the problem of sorting / organizing music that has a known composer and multiple recordings by different musicians / orchestras.
Even though people play covers in popular music styles, people rarely care about organizing the music that way. I don’t think, “I want to hear Yesterday” and then look up a list of covers. But I do think, “I want to listen to Rite of Spring” and then look up a list of recordings.
Even though composers are a big deal in Jazz, I still usually care more about the performer. Most of the time, I’m not going to ask the computer for a list of Autumn Leaves recordings.
And some musicians do rerecord popular songs, which means you've got several different performances of the same thing. This isn't even that rare with live albums.
I mean sure for the most recent pop music it won't be a problem, but that's a very narrow window of time.
I do think it kinda makes sense, because classical music listening is more oriented around certain performances by specific musicians, rather than the piece itself, which normal music platforms aren't well suited for.
But that isn't quite unique to classical, which as you've pointed out is going to be a denotational quagmire and almost certain to piss people off. Hopefully they take the dumbly funny but also appropriate approach of just also putting jam bands, gospel and dj sets in there, which share this performance-orientation with classical music.