The quoted description is correct. The boot ROM loads code from flash: the "second stage" loader. That loader then (usually) configures the RP2040 to execute the actual application directly from flash.
But the "Easter egg" function discussed in this HN thread is not inside any code loaded/executed from flash. It is inside the boot ROM (as I've repeatedly stated); and that is indeed read-only memory, i.e., it cannot be modified except by manufacturing a new chip revision.
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The quoted description is correct. The boot ROM loads code from flash: the "second stage" loader. That loader then (usually) configures the RP2040 to execute the actual application directly from flash.
But the "Easter egg" function discussed in this HN thread is not inside any code loaded/executed from flash. It is inside the boot ROM (as I've repeatedly stated); and that is indeed read-only memory, i.e., it cannot be modified except by manufacturing a new chip revision.