Now let me answer to your post.
Firstly Vasilije Petrovic whom has written this book that contains this letter is not a Macedonian but rather a Montenegrin. I hope that answers the first part of your post.

Secondly, Vasilije clearly differentiates between the Macedonians and the rest of the people he names.

Petros the “Greek Macedonians” that you speak of were a small minority and they were not calling themselves by the name you gave them, they were calling themselves for ROMEOI(meaning Romans), and nothing else. So please do not mislead people.

I hope I have answered your post.

Everyhting else seems correct. The author does not speak of obsolete people like Thracians, and the prototype proves that the person was a genuine Balkaner.

The only problem thus, is that we do not know who those Macedonians were. There might have been your folks, or Greek Macedonians, who used the legacy of Alexander the Great as well, no later than half a century later. Your author does not describe those Macedonians, and you get no proof of who these were, just a name. I am afraid that this is not sufficient evidence…