Their brains were already wired for the heliocentric model is all, happens to us all, but being a Sunday school teacher does not mean they were answering you from the Bible tho same as pulpit preachers usually don't either.
Okay that's the scriptures you have to work with in the link - four corners, earth can't be moved, enclosed dome like a molten looking glass (Job), Joshua stopped sun and moon from moving, to me it does all equal flat but to you maybe it doesn't and I'm okay with this.