Cannot or Can Not?
According to Merriam Webster's Dictionary of English Usage, "Both spellings are acceptable, but cannot is more frequent in current use. Chambers 1985 insists that cannot must be used in British English unless the not is to receive particular emphasis. A couple of American sources (Oxford American Dictionary 1980, Trimble 1975) mention that the two-word form can be used to indicate special emphasis.... "Can you jump? I can not, says the sergeant" (219).
Are you arguing that OP was trying to indicate special emphasis? Because according to this source, "can not" is acceptable but is not the most appropriate choice here.
Did you read the passage, or just infer your own meaning into the text?
"Both spellings are acceptable, but cannot is more frequent in current use."
Everything that follows is a caveat that doesn't have to apply or a corollary that isn't applicable.
I cannot believe you don't understand this concept.
I can not believe you don't understand this concept.