Q. Is our son's college apartment that we paid for from our 529 considered a college expense, as in the "room" in the "room and board" entry line?
A. Yes.
Off campus rent and food are eligible expenses for a 529 distribution, but the amount is limited to the lesser of your actual cost or what the school charges on campus students for R&B (technically the schools "allowance for cost of attendance" for financial aid purposes).
References:
https://www.glassjacobson.com/blog/529-off-campus-housing/
http://turbotax.intuit.com/support/iq/Education/Information-about-Form-1099-Q/GEN12272.html