The expertise offered here is "how to build a website". If the client is insisting that the dev use a specific javascript library, that would be odd.
The client here is just requesting specific content on their website, similar to someone requesting a granite countertop in their kitchen; that seems fine, even if its not particularly classy or aesthetically pleasing to the contractor.
It's more similar to someone asking for a cardboard countertop - any contractor would be well within their rights to tell them it's a bad idea and would be negligent if they didn't.
Do we know that for a fact? You described them as a "web development consultant", but I couldn't tell for certain what their exact role on this project was. Their services page (https://www.nicchan.me/services/) lists both "Web Application front-ends" and "translate your designs into a scalable system", so I think they offer a range.