Christ is Truth, and insofar that the Orthodox Church is the body of Christ, then it is the fullness of the truth. To say this does not mean that outside of the Church there is nothing but lies: everything Orthodox is true, but that doesn't mean that everything true is Orthodox. Abiding in the Truth (Who is Christ) means we can discern what is truth and what is not, whether it is "within" Orthodoxy or not.
Having said all that, the Orthodox Church I describe as being "all true" refers to the Holy Spirit's work within her: the teachings, the good fruits, the Liturgy, the prayers, the hymns, the iconography, and so on. The people who make up the body are, as they have always been, at differing stages of healing: some, the Saints, are practically perfect icons of Christ, but others are not. Whilst "everything Orthodox is true", individual Orthodox Christians are still fallible and therefore liable to mistakes; being Orthodox doesn't mean someone is even immune from deliberately lying about something.
This links back to your OP where people ask if such-and-such a writing is from an Orthodox author. Even if it is from an Orthodox Christian, it is no guarantee of it being true -- the writing will only be true insofar as it is in line with the "mind" and "life" of the Church, i.e. the beliefs of the Church throughout all ages and grounded in the teachings of Christ.
It's always nice to quote a source for any copy-and-paste though