Is this person a dependent?

Do they have any income?

If they are not a dependent and they received Advance credit (column C of the 1095-A), yes, they are required to file a tax return.

If they are not a dependent and they did NOT receive Advance credit (column C of the 1095-A), no, they are not required to file a tax return.  If their income is below 100% of the Federal Poverty Level, they probably won't qualify for any credit even if they choose to file a tax return (but as with most tax law, there are exceptions).