In the U.S., the regulatory requirement related to exit row seating is found at 14 CFR 121.585 - Exit seating, which contains the following two elements related to some of the discussion here:
Sec. 121.585 - Exit seating
(b) No certificate holder may seat a person in a seat affected by this section if the certificate holder determines that it is likely that the person would be unable to perform one or more of the applicable functions listed in paragraph (d) of this section because--
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(4) The person lacks sufficient visual capacity to perform one or more of the applicable functions in paragraph (d) of this section without the assistance of visual aids beyond contact lenses or eyeglasses;
(5) The person lacks sufficient aural capacity to hear and understand instructions shouted by flight attendants, without assistance beyond a hearing aid;
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Full text of 121.585 here...
It would seem to me that either the crew misinterpreted their operating manual or the operating manual is more restrictive than the regulatory requirement. Then, of course, there is always
14 CFR 382 - Nondiscrimination on the Basis of Disability in Air Travel...
