Good catch. There was speculation in the baseless thread: Maybe Sony had RT plans much earlier than thought, and DXR was a reaction also to this, not only because NV was ready at the time.
Personally i now think Sony has a different and custom RT solution than XBSX + AMD, hinted by those points:
DXR came totally surprising out of nothing. NV exposing this just by API extensions would have been expected, but full integration into DirectX although there was only one HW vendor with support, without any announcement before is just suspicious and seems rushed.
The Github leak mentions AMD RT for XBSX but not for the PS5 chip.
Using completely a different term, 'based' instead 'accelerated' maybe also hints Sony had RT in mind before RTX came up.
It is possible they do have a different solution for ray tracing and that's why they used different terminology than both AMD and MS, but as iroboto pointed out above Cerny did clarify that it was accelerated ray tracing. Either way I'm excited to see what developers can do with both consoles. Digital Foundry has a great video showing how raytracing, even when applied to a simple game like Minecraft can make a big and noticeable difference.