There are a number of ways.
Hard to tell from only seeing what is written, would take some hands-on examination of information exposed by both kernels (if, indeed, you have two different kernels).
The general area to look in is the clock and power speed controls. Those are exposed in the /sys tree of the file system.
The "main" kernel, kernel modules in the "main" file system, and settings in configuration files of the "main" file system will have the machine set in "Bragging Rights, Aggressive, Low Power Mode".
(That isn't the Linux name for it, that is what Amazon Marketing uses it for.)
The "Diags" kernel, kernel modules in the 'diag' file system, and setting in the configuration files of the 'diag' file system have no need for that mode. In fact, it may not even be available in the kernel built for the "Diags" system.
The machine is not expected to have any need to run for months on battery power in "Diags" - -
So it is reasonable to expect that in that boot mode, the clock and power scaling is probably set towards the "performance" end of the setting range.
OR - clock and voltage control might not even be included in that kernel.
So yes, it is possible.
It would take hands on the keyboard in both modes to run down if that is happening or not.