I’m not really sure that there is a widely–recognized name for these things in Emacs Lisp. The language has grown and changed over time, and things have been added to the language as needed. You could look into the version control history of the Elisp manual to find out more about how it has changed over time. I am sure that they would consider improvements to it as well. You could fix it by simply inserting another sentence after the #<…> example saying something like “The # character also introduces these other syntactic elements recognized by the reader”. Also, I have no idea why the character syntax (?C) is even on that page.
The use of # in Lisp syntax is influenced by other Lisps such as Common Lisp, where the # character indicates the use of a reader macro. The Common Lisp Specification calls it a non–terminating dispatching macro character, which is a long–winded way of saying that the character after the # tells the reader which macro to invoke. But notice that it never actually names the syntactic elements themselves; it just says that they all dispatch to reader macros.
hash markor simply
M-x report-emacs-bug. If the doc wants to use or introduce such a term then its uses of the term should be clear/consistent.
#has many names. In addition to "number sign" and "hash" it is also called "pound sign" and "octothorpe". (BTW a "hashtag" is a "tag" that starts with a