That is a mistake on the IRS' part and is probably getting people confused.  They shouldn't have to file a return to be eligible.

§6428(f) is the subsection that deals with Advance Refunds and Credit of Recovery Rebates.  Paragraph (5)(b) specifically provides that the IRS will use information from the SSA-1099 to issue these payments where no returns are filed by these recipients.

6428(f)(5) Alternate taxable year.—
In the case of an individual who, at the time of any determination made pursuant to paragraph (3), has not filed a tax return for the year described in paragraph (1), the Secretary may—

6428(f)(5)(A) apply such paragraph by substituting "2018" for "2019", and

6428(f)(5)(B) if the individual has not filed a tax return for such individual's first taxable year beginning in 2018, use information with respect to such individual for calendar year 2019 provided in—

6428(f)(5)(B)(i) Form SSA-1099, Social Security Benefit Statement, or

6428(f)(5)(B)(ii) Form RRB-1099, Social Security Equivalent Benefit Statement.