He still was a ruler. There is nothing in Orthodxy which says rules of countries can't become Saints because of the job. Don't the Orthodox also venerate St. Olaf of Norway, St. Edward the Confessor of England, and St. Stephen of Hungary? Funny that so many Saints were then in the world around AD 1000-1050 as rulers of countries.
Sts Miltuin, Lazar, Dushan and all the other rulers. As I said I don't know what criteria are used to make someone a saint because many a saint weren't very saintly and still made the rollcall! I believe the Church of the East and the West do not use the same criteria. I think of saints in terms of Mother Teresa -- a woman who owned nothing but a Bible and a pair of sandals, and helped people as muchas she could. Anyone in power simply doesn't seem to compare to that.
Maybe you can shed some light on this.