The IBIS model you are using is not most recent and indeed contains model selector "lvcmos" for these pins.Your understanding is correct, impedance is fixed and, therefore, this model selector is not necessary. For QSPI pins actual model will be model with *fsr* suffix.
Please submit a ticket to online technical support to get most recent IBIS model, which does not have this problem.
How to submit a new question for NXP Support
Have a great day,
Alexander
TIC
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