[COMPONENT][Posting] Clarify use of cache in note replies when posting

components/Posting/Posting.php

@@ -335,6 +335,8 @@ class Posting extends Component
         // Update replies cache
         if (!\is_null($reply_to_id)) {
             Cache::incr(Note::cacheKeys($reply_to_id)['replies-count']);
+            // Not having them cached doesn't mean replies don't exist, but don't push it to the
+            // list, as that means they need to be refetched, or some would be missed
             if (Cache::exists(Note::cacheKeys($reply_to_id)['replies'])) {
                 Cache::listPushRight(Note::cacheKeys($reply_to_id)['replies'], $note);
             }