Where do Slavs get the idea of Macedonians being seperate from the Greeks?

There are 2 Macedons.  One Macedon is part of the former Yugoslavia and the other is located in the north eastern part of Greece. Both are inhabited by different ethnic groups.   

Although on the Greek peninsula Macedonia was not really part of classical Greece. Before the 4th century BC, Macedonia was a small kingdom outside of the area dominated by the great city-states of Athens, Sparta and Thebes, and briefly subordinate to Achaemenid Persia.

Alexander the Great fullfilled the third empire of Daniel 2 The Bible considered them Greeks. Today Macedonia worship Islam while Athens are Greek Orthodox

First of all, Macedonia today isn't where Macedonia of old was located. In fact, Macedonia's appropriation of the name has been a matter of some controversy because of how it's historically inaccurate. Second of all, Macedonia today is peopled predominantly by Slavs, whereas Greece is peopled predominantly by Mediterraneans. Third of all, Ancient Macedonia was ruled by the Greeks, Alexander the Great being Greek because of both of his parents, Philip and Olympia, being Greek, which is why he received a classical Greek education and why all his generals were Greek, like Hephaestion, his favorite, and Ptolemy, whom he bequeathed Egypt to.