“Find references” shows you all direct callers of the selected method. “Call hierarchy” in contrast shows also the callers of those direct callers, and the callers of those, … and so on.
So the output is only identical, if direct callers of your selected method do not have any callers themselfes. Just try both commands on some larger code base and you will immmediately see the difference, like in this screenshot:
If you wonder why there are two such features, if “Find references” is basically just a subset of the “Call hierarchy”: Find references works really fast, so you can use it all the time without any waiting for results. The call hierarchy on the other hand takes more computation time and therefore may interrupt your coding workflow.