That might be what the Chubb call centre have been trained to say, however, I think they are on shakey ground as there is no definition provided in the T+C's that defines the word corresponding to mean "FF points came from MR".
My read of eligibility criteria 4ii is outbound flights payed with points must be one of Amex Membership Rewards or frequent flyer points. The most important part of this sentenance is the or indicates one or the other, but not both. In terms of the word corresponding, there is nothing in this sentence to indicate the that the frequent flyer points must correspond with the amex membership rewards points, rather my read is the amex or frequent flyer points must correspond to the full amount of the outbound ticket.
I'm not a lawyer, so all this is my interpretation, but it multiple members here have different interpretations than it stands to reason that the terms and conditions are ambiguous, hence Chubb is on shakey ground.