I'm really sorry to have offended you. I'm careful always to be respectful of other people's beliefs.

A major component in the practice of Orthodox Christianity is the attainment of Theosis. It is even said that it is the purpose of man. If that is the goal, to participate in the divine nature; to become so much like God that you participate in His nature, and there are practices or rituals to facilitate that goal, then it can be considered a mystical tradition.

It's likely that the term carries some extra baggage for you, being associated with magical practices or polytheism. However mysticism refers to the goal (some sort of union with God, not necessarily complete union as that's likely impossible) and any reference to practices (such as magic) are external to the term.

The way the term is used in your culture or in the groups you surround yourself with, likely devout Orthodox Christians, is different than it is used in my environment. I am deeply devoted to the goal of mysticism (some level of union with God), both through study and practice, and surround myself with such people.

I do agree that Orthodox Christianity has a strong claim for being the "one, holy, catholic, and apostolic church" and even hold that as my opinion. We do not disagree there and by labeling it a mystical tradition I wasn't suggesting it was an offshoot or an outlier in Christianity. In fact I believe it to be the truest branch of Christianity (while not in a way that makes other Christians less Christian) and have considered converting.

Some extra reading that might be helpful:

https://www.ancientfaith.com/specials/eastern_orthodoxy_and_mysticism/orthodoxy_and_mysticism_part_1

http://orthodoxinfo.com/general/lossky_intro.aspx

Edit:
https://en.wikipedia.org/wiki/Mysticism