Who was it that Luke followed and Learned from?
Hebrews is also generally attributed to St Paul.
The Orthodox do not suspect the saints are actually dead, instead we acknwoeldge that the saints, even those departed from Earth, are alive in heaven, and still pray. (The notion that folks who go to heaven stop praying is crazy).
While Hebrews is believed to have written by Paul, some feel that the author was actually Barnabus. No one really knows except Christians (well, most) believes it to be inspired by God.
But all this does make one wonder why the Church doesn't view believers, living now here on earth, as saints when the evidence in scripture calls them that?