Question: How does the block keyword work ?

Answer: The block keyword in the SECTION directive of the linker command file tells the linker to

Make sure that the output section either does not cross a 0x10000 page if it is smaller than 0x10000 in length,

OR

If it is larger than a 0x10000 page, make sure that it is aligned to start on a 0x10000 page. It does not tell the linker to make sure the the output section is not longer than 0x10000.