Not that it matters much for the rest of the story, but I do not believe that is true. I think if there is a boot loader on the SD card, that takes preference over the one in the SPI NOR flash.
I had a similar issue where I was getting confused that it would not boot from SD card, but it turned out the u-boot on my SD card would choose to boot from NVMe instead of from SD.
If you’d like to know more, please see [SOLVED] Boot problem (my own fault; not USB PD related)