I'm pretty sure the text below the "Buy Now" button is autogenerated, if it doesn't mention "your purchase also comes with a Steam key" then you're out of luck. Presently you can get the DRM-free and Steam key combo if you get it from the Humble Store, though.
Good to know. I remember that Dicey Dungeons didn't give a Steam key till it left early access, and then sent everybody one. That was nice. I'd like to support Noita on Itch to make sure the devs get the best cut of the sale. I'll probably do that ANYWAY, but an eventual Steam key would be good to have.