It bears checking, but that's my impression from what I've read over the years.
So while I don't have anything concrete right now, my understanding of the situation doesn't rule out Serbia's wanting/needing to procure weapons/munitions from the international market, and Greece had both the motive (orthodox fraternity) and opportunity (location) to benefit from Serbia's needs.
That's a favorite fisction of the liberal Hum Warriors. Maybe the Greeks just don't like unjust wars in their neighborhood--would you?