Yet it's one of the top questions on their announcement page and they won't clearly answer it.

Likely because most people think "source available on GitHub" = "open source", so they're just answering the low-hanging-fruit even if the question is technically incorrect. They don't claim to be open source anywhere, and I haven't seen them claiming to be open source since they relicensed to the BUSL over 5 years ago. I don't think there's malice here.