Depending on the context, you might call that person an electrician, or an auto mechanic, or a plumber, or a computer technician, or a housewife trying to change a battery.
HTML is a tool. A job title/description tends to be more about what you are expected to accomplish.
This can be confusing, because there is such a thing as a "C++ developer." Well, yeah, but what you really are is an application developer who uses C++. Your job is to develop applications. It just so happens that C++ is the primary (maybe even only) tool you need to accomplish that job, so that's what you get called.
I think the reason this particular skill has not acquired a standard job title is that HTML, by itself, is not really a tool you can use to accomplish a whole lot. To accomplish a complete task, you will need to use it in conjunction with graphic design tools, if you're designing an interface, or with database tools if you are designing an app, or something else.
So I'd say it depends on what you are expecting them to use HTML to accomplish, and what other skills they will need in order to accomplish that task.
As for whether HTML is a complete skill set -- well, imagine applying for a job as a plumber and saying, "well, I can't use a wrench, but I can use a screwdriver..."