I'm not buying it, either.

The stone is a decree praising the king of Egypt (Ptolemy V - 206 BC-181 BC). The Greeks and the Egyptians were the dominant literate cultures in the area and there was no need to write the text in languages not in common use in the city where it was set up.

By that time, Macedonian coins had been using the Greek alphabet for well over 100 years:
[www.alexandercoins.com]

There is absolutly no reason to write Macedonian in a script that the Macedonians never used.

Verdict: Truly Bad Scholarship.