Yes it is correct, and I fully stand by it. The instructions on the new I-134 Declaration of Financial Support is originally meant for NIV applicants. You omitted pertinent section of the instruction you quoted. The entire section says: '
You may file this form on behalf of yourself or on behalf of a B, F, or M nonimmigrant requesting extension of stay or change of status" - meaning the form was originally designed for use in support of NIV applications. Yes, it further says the form may be requested by DOS in certain circumstances (such as DV, K1, or SB). It isn't unusual for USCIS to provide conflicting or unclear instructions on their forms for all applicable circumstances. Form I-485 is an example which readily comes to mind. The instructions on that form says DV based AOS applications require no financial documents, yet the IOs routinely ask for financial documents at the time of the interview.
Someone applying for an IV listing their current annual income (earned outside the US) to demonstrate self sufficiency makes makes no sense considering that income will not be ongoing upon relocation to the US. Using that income to demonstrate self sufficiency makes sense in support of a NIV application. This is the same reason current income earned outside the US cannot be listed on form I-864 for family sponsorship for instance because that income will not be ongoing, unless the income is from a US company and the person being sponsored will continue with the same employer following their relocation to the US.
If Simon is recommending folks could fill out the form themselves as against having a sponsor fill it out (I haven't watched the video, so I really cannot speak to it), my guess is he's making that call as an exception in certain cases.
Take a look at section
(3)(U) Use of Form I-134, Affidavit of Support of the 9 FAM 302.8 (U) PUBLIC CHARGE - INA 212(A)(4), the DOS Manual for COs (this section deals with the certain circumstance the DOS may require the use of an I-134 referenced earlier on above) - it talks about "
the sponsor", nothing about the applicant for an IV filling out the form themselves.