I have no idea how it determines the newest, but the saved
kernel is saved in the grubenv file which you can edit
with the grub2-editenv command (but only after getting
hundreds of errors because the command line syntax
for editenv is very obscure and easy to scre up :-).
Thank you.
The confusing thing is that the output of 'grub2-editenv list' and grubby both
show that currently the correct (newest) kernel is the saved kernel. This kernel
isn't what is actually selected at boot though!
This thread has been helpful to confirm that I'm not crazy!