Yes that did not work because toc_float is not an argument of distill_article().
Currently floating toc is not supported in distill. Only this toc:
Table of content is always placed the same in distil article and I don't think this is a compatible feature (yet ?) in distill.
The layout / theme used by distill is not the same as basing Rmarkdown, so the JS code for floating toc of Rmarkdown is not used here. Sorry.