Allow me to throw in my 2¢. Are all Xtians condescending? Absolutely not. Are all Xtians arrogant? Absolutely yes.
Not all Xtians will exhibit outward expressions of superiority, or patronize others, or show contempt as though someone is beneath them. Granted, a large portion of them do this, but in my personal experience, it's not universal. Just because someone's a Xtian, or for that matter an atheist, doesn't automatically equate into being an asshole. On the other hand, irrespective of being a Xtian or an atheist, someone can just simply be a horse's ass because that's who she/he is.
Arrogance is an entirely different story, in my humble estimation. The basic belief of Xtians boils down to the commonly held idea that the universe, and creation, owe them something just because they were "created." The all encompassing, omnipotent, omniscient, omnipresent entity they refer to as god, takes a personal interest and active role in their individual lives. Because after all, aren't they just f&*king "special?" They can telepathically call on the creator and manager of the 13.4 billion light year sized known universe to insure they find their car keys, get that promotion, birdie the 4th hole at the golf course, or intervene and save their raggedy hide in a life threatening situation. And, as an extra added bonus, god actually cares about whom they have sex with, in what position, and when they have constipation. Don't believe me? Just take a look at the contorted face of a devout Xtian praying with all his might, and tell me you don't wish his god would hand him a box of laxatives. (OK, that last one was a bit condescending on the part of this atheist).
Beware of solipsism. Don't ever think you are the center of the world. Be very careful of assuming that you are the object of a divine design. That there's something special just about being you. That that's all you have to prove - that, why wouldn't a person such as yourself have God on their side; Why wouldn't it be - 'of course God would care who I slept with, what I ate, what holy day I observed, why would He not? Surely that's why the heavens are arranged in the starry beauty and array in the form they take.' -- You are forced to wonder, if maybe - even though it's a less beautiful thought - it could be that the galaxies are not arranged with you in mind. Christopher Hitchens.
So called "mind reading", when another is certain they know your thoughts or intentions better than you do, is among the most annoying forms of dysfunctional communication. Were this my friend, if I even wanted to continue the discussion (I wouldn't), I'd address this communication error rather than the original disagreement. It's not only Xians who make such unwarranted judgments.
I've gotten this line before myself. Their splintered logic goes something like this: When a person asks Jesus into their life, the Holy Spirit also comes into the believer's heart. This, to them, apparently makes going from Christianity to atheism an impossibility since the spirit of God is supposedly residing inside the person's soul, and if that's true, the believer would never consider giving up their faith or even questioning it. Thus, they just claim that we former believers were actually deluded and that we didn't really have a genuine conversion experience and never truly had the Holy Spirit. Of course, the arrogance of the person you mentioned just echoes the general arrogance of believers in Jesus generally, thinking that God created the world with them in mind and that the almighty God of the universe is on their side. At least scientists and religious skeptics are humble enough to admit we don't have all the answers, and that asking questions is better than claiming to have a grasp on absolute truth.