That one’s not really a red flag. If they keep all of the same assets and lighting settings, UE5 will look damn close if not identical. Updated code doesn’t mean it magically updates the graphics, though I bet plenty of UE-sourced assets have easy upgrade paths.
For an example of a game that doesn’t suck that did this, see Satisfactory. It looks nearly the same. Though I think some things have improved slightly, since they at least enabled a few things.