They are not "fully unrelated". The backquote syntax for constructing lists was primarily designed for macro programming. See the paper Evolution of Lisp by Guy Steele and Peter Gabriel:
"Macros took a major step forward with Lisp-Machine Lisp, which consolidated the various macro-defining techniques into two standardized features that were adopted throughout the MacLisp community and eventually into Common Lisp. The macro defining operator DEFMACRO provided list-structure destructuring to arbitrary depth; the backquote feature provided a convenient and concise pseudo-quoting facility. [ ... ] Backquote and DEFMACRO made a big difference. This leap in expressive power, made available in a standard form, began a new surge of language extension [...]" [3.3]
For example one can write a vector of three elements, where the second element is computed:
Backquote list forms happen to be used in some macros as a kind of template forms. Macros can be defined without them and backquote forms are also used elsewhere in Lisp.