Quote:

"So God made the expanse and separated the water under the expanse from the water above it." (in the Hebrew original it's not "expanse" but "vault" as in architecture).


--One more point here ,I used Strongs Concordance , the Hebrew word used here for firmament is raqiya, pronounced raw-kee-yah, it does indeed mean 'expanse' or more literally 'the visible arch of the sky'

I think your source might be interpreting an arch to exclusively be used in architecture.