Bill has been doing this for years, and I would be almost willing to guarantee that he has heard of this before. yes our trucks are designed to run 87 octane, but he knows how to advance the timing and other setting to compensate for the 91 or 93 even.
There are a few people on the forum, including me, that just get the 87 because that is the recommendation from ford, and it is cheaper, but i have never heard any problems with plugs or knocking using 91... and I thought higher octane prevents knocking since knocking is when the gas detonates too early
so dont freak out unless something bad happens, and if you are in doubt then you can switch back to canned tunes until you get them switched back to 87 if you feel the need to go that way