How is it a factual error?
I can have faith in anything I want, just because I believe it to be true wholeheartedly doesn't necissarily mean it's true.
Do not confuse faith with fact. Faith MAY be fact, but by it's very nature you can't prove one way or the other, that's why it's faith.
Are you saying evolution is "fact"?
The appropriate maxim is: "Seek out people who claim to be searching for the truth; run from people who claim to have found it."
"How is it a factual error? . . .you can't prove one way or the other, that's why it's faith."
Your argument rests on the premise that anything one human cannot prove to another cannot be called a fact. What you overlook is that, when God demonstrates His existence to a person, then that person knows (not believes, knows) that God's existence is a fact and not solely a matter of faith.
When God does that, and it seems it happens far more often than even most believers think, He does it in such a way as to leave mankind's free will intact -- that is, in such a way that people are able to generate objections, doubts, and outright disbelief if they are so inclined.
Still, for many people walking the earth today, and many more throughout history, God's existence has at some point become fact and not a matter of faith.
Further, those who study accounts of such cases and decide that they make a compelling case are engaging in no more flights of fancy than historians who look at accounts of ancient events and find them credible, or modern investigators who look at patterns of reports and find them credible. The only difference is that any event that has to do with God is a priori deemed implausible or impossible, which is hardly scientific.
People are frequently convicted in courts of law on the basis of eyewitness testimony, which is stronger if corroborated by more than one witness, but eyewitness testimony of God's existence is rejected out of hand because of that same a priori assumption.
When it comes to direct contact with God, many people seem to regard it as open-minded to take the position, "It hasn't happened to me, so all such reports must be false." Others, hearing that, say, "It hasn't happened to me either, so he must be right about it being false."
Pretty soon you have a whole, informal league of people who reject all accounts of such things on the grounds that, "It must be false, because it's impossible." And this they deem open-minded, rational, and scientific.
Go figure.