That's not true at all. If someone gives you a gold bar right now, would you be able to tell if it's real or not? What if, for example, it's steel on the inside coated with a thin layer of gold. Or the gold has a low purity, etc. This is why there are specialists (who are very expensive) who can use special tests to check if it's real (and even then it's not 100%).

It's easy to tell if the Bitcoin that you just received is real or not. (Definitely much easier and cheaper than with gold).