Almost. The intended use is for Ctrl-F to initiate an on-page search, and Ctrl-G to highlight the next match during a search-in-progress. If you press Ctrl-G when there isn't a search in progress, the developers decided to allow the fallback behavior to be to begin a search.

So they're interchangable in a specific context (no search in progress), but once the page search begins, their roles are different.