You seem to be correct. Not that much visible from the outside, but yes it seems like they always ran on Azure, from the 2018 launch. (Apologies for the disinfo, although I qualified it with the "I assume".)
Pre-launch I seem to recall using an entirely different product with the same name, that supported CUE or HCL and had a better gui editor. I think post acquisition they scrapped it for the current (and IMO) worse reskin.