Huh. Well I'll be dipped, that does indeed appear to be DSD1024 being bitstreamed.
I'm fairly sure that support for DSD1024 likely wasn't intentionally added because it was never added to any of the MC release notes and I've never seen Matt, Hendrik, Bob or Jim mention it at all (other than a couple years ago where they rejected the notion of it). If I had to guess with a total shot in the dark guess, maybe there was a general change in how bitstreaming works in MC (I seem to recall Bob or someone at some point within the last few months mentioning some sort of change done to bitstreaming) that perhaps had the side effect of allowing DSD1024 bitstreaming to 'work'. Perhaps the most logical reason is when it's set to bitstream all DSD sample rates it literally does just that, it just tries to send whatever DSD bitstreamed as-is with no limit at all, even if it's above DSD512, which in honesty *could* be considered a bug if that's the case. Unless Jim, Matt, Hendrik or Bob say otherwise, I actually don't they intended for DSD1024 bitstreaming to work in MC. Does it work in the last build of MC31? I wonder when it started to work...
Kinda reminds me how you can get MQA working through MC even though it doesn't support it at all as long as you use no DSP whatsoever and have volume at 100%.