Your parents if getting no refund, and having no balance due, would not have to file a tax return for 2016 tax year.

Your parents, assuming they are over 65 years old, would not have to file a tax return if their taxable income is less than: $23,200 (Personal exemptions of $4,050 each, plus Standard Deduction of $12,600 + $1,050 + $1,050 due to over age 65).

Note:  Social security does not get added to taxable income if they have little other income. 

You did the right thing by entering it and finding out if they had any balance due.