The naming of things is pretty confusing. Async queue, send once, and send many all threw me off and aren't good descriptions for what we are trying to do. I hope this isn't reflective of the company's actual code base. A bit of a red flag.
It also is framed as not a JS question but then the interviewer wants an answer that only makes sense in JS. It also isn't even modern JS. A couple more red flags there.
I dislike questions like this in general, but I've done interviews where they facilitated a decent conversation. It really depends.
It is also just a blog post so hard to infer a lot about the author's actual interview style. Maybe it is great and collaborative. It does remind me of some of the worst engineers I have ever worked with and their interview style though...