Clarify comment

housekeeping/src/main/groovy/whelk/housekeeping/BulkChangePreviewAPI.java

@@ -172,7 +172,7 @@ private Map<?,?> makePreviewChangeSet(RecordedChange recordChange) {
         thingBefore.put(RECORD_KEY, recordBefore);
         thingAfter.put(RECORD_KEY, recordAfter);
 
-        // However when the diff is computed we need "@graph form", hence the record copy at @graph,0 in both versions
+        // However when the diff is computed we need "@graph form", hence the same record copy at @graph,0 in both versions
         var beforeDoc = new Document(Map.of(GRAPH_KEY, List.of(recordCopy, thingBefore)));
         var afterDoc = new Document(Map.of(GRAPH_KEY, List.of(recordCopy, thingAfter)));
         var id = (String) recordCopy.get(ID_KEY);