If other Christian churches' sacraments were just as valid, they'd be Orthodox.
The major difference between Orthodoxy and other expressions of Christianity is not in the sacraments alone. If it were, there would be little need to convert unless one were a junkie for elaborate ceremonies.
Orthodoxy emphasizes aspects of Christianity that are almost entirely unknown when compared Christianity as it is understood and practiced in the west. Consequently, it comes as a profound revelation and delight to western seekers. I would go so far as to assert that most American Christians have no idea what, in fact, Christianity is. It's a vast subject--one not well served by a mere comment.
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Your priest may have meant that in a very broad sense; eg, a married Christian is married by the Church, regardless of the denomination in which he or she was married (provided it is acknowledged as a mainstream Christian denomination). The covenant is between the persons being married and God; the denomination is secondary. The church also accepts Baptisms from some other--not all--churches.
As william (below) suggests, the Orthodox are quite comfortable with ambiguity. That, in itself, is very un-Western. Very.
